Not sure if its just me or my configuration.

I am basically checking apple pay support on iOS and once thats done, I am opening the payment dialog using showPaymentSelector

After successful payment I get nothing, no data in return.

Map<String, dynamic> data = await _pay.showPaymentSelector(
    provider: PayProvider.apply_pay,
    items:[......]
);

Some payment providers supported accept a list of items to show and calculate the total price of the transaction, while others simply take the total price.
Create a lightweight class to hold price information to pass (in the form of a list) to the widget for the price calculation.

Hello I get the following error when trying to open Apple Pay

Unhandled Exception: PlatformException(paymentError, Failed to present payment controller, null, null)
#0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:581:7)
#1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:158:18)

#2 PayMethodChannel.showPaymentSelector (package:pay_platform_interface/pay_channel.dart:64:27)

#3 _PurchaseScreenState.payment (package:lalamu/pages/purchase/view/purchase_screen.dart:42:33)

Hi,

Instead of card payment i want to enable in app gpay for UPI payments(in India). Is it possible?

I tried to run flutter pub get in flutter-plugin/pay/ but i'm getting this error
Because every version of flutter_test from sdk depends on test_api 0.3.0 and mockito >=4.1.2 <=5.0.0-nullsafety.7 depends on test_ api ^0.2.19-nullsafety, flutter_test from sdk is incompatible with mockito >=4.1.2 <=5.0.0-nullsafety.7. So, because pay depends on both flutter_test any from sdk and mockito ^4.1.3, version solving failed.
Edit: found solution for this issue it is because the version used in pay/pubspec.yaml is mockito: ^4.1.3 which should be updated to mockito: ^5.0.0

When i add postalAddress to my payment profile like this:

{
  "provider": "apple_pay",
  "data": {
    "merchantIdentifier": "merchant.mxxxxx",
    "displayName": "xxxxx",
    "merchantCapabilities": ["3DS", "debit", "credit"],
    "supportedNetworks": ["amex", "visa", "discover", "masterCard"],
    "countryCode": "DE",
    "currencyCode": "EUR",
    "requiredBillingContactFields": ["postalAddress"],
    "requiredShippingContactFields": ["emailAddress", "name", "postalAddress"],
  }
}

the Apple Pay sheet shows and lets me select a shipping address and a payment address.

I use this ApplePayButton:

pay.ApplePayButton(
          height: 50,
            paymentConfigurationAsset: 'apple_pay_payment_profile.json',
            paymentItems: _paymentItems,
            style: pay.ApplePayButtonStyle.black,
            type: pay.ApplePayButtonType.buy,
            margin: const EdgeInsets.only(top: 15.0),
            onPaymentResult: onApplePayResult,
            loadingIndicator: const Center(
              child: CircularProgressIndicator(),
            ),

The paymentResult in onApplePayResult contains the name, email and other data but no address.
How can i obtain it?

Launching lib/main.dart on AOSP on IA Emulator in debug mode...
lib/main.dart:1
Note: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/local_auth-1.1.6/android/src/main/java/io/flutter/plugins/localauth/LocalAuthPlugin.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
e: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.4/android/src/main/kotlin/io/flutter/plugins/pay_android/GooglePayHandler.kt: (172, 27): Expecting a parameter declaration
e: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.4/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (40, 28): Expecting a parameter declaration
e: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.4/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (56, 52): Expecting a parameter declaration
e: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.4/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (41, 79): Expecting a parameter declaration
e: /Users/ajaylee/development/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.4/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (55, 67): Expecting a parameter declaration

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':pay_android:compileDebugKotlin'.

Compilation error. See log for more details

• Try:

Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 48s
Exception: Gradle task assembleDebug failed with exit code 1
Exited (sigterm)

what to do now

==========================================================================================
sorry for the duplicate

problem has been fixed by changing the min sdk to 19 and kotlin version to 1.4.20 and com.android.tools.build:gradle:4.1.1

With Flutter 2.2, the web platform reached a stable release.
Include the integration for Web as part of this plugin with the two providers supported for mobile (Apple Pay and Google Pay).

I'm using Apple/Google Pay to generate a Stripe's charge, then I'm passing the token to our backend that takes care of the payment process.

Here's the GPay flow:

Inside the google_pay_config.json we've all infos about Stripe:

"allowedPaymentMethods": [
      {
        "type": "CARD",
        "tokenizationSpecification": {
          "type": "PAYMENT_GATEWAY",
          "parameters": {
               "gateway": "stripe",
	       "stripe:version": "2018-11-08",
	       "stripe:publishableKey": "stripe_key"
      }
   }
]

Then I'm creating all the PaymentItems, getting a PaymentResult and finally from PaymentResult I can get a token to pass to the backend to complete the payment.

final token = paymentResult['paymentMethodData']['tokenizationData']['token'];
final tokenJson = Map.castFrom(json.decode(token));
String tokenId = tokenJson['id'];

How can I obtain that token using Apple Pay since I couldn't find any way to specify the Stripe data inside apple_pay_config.json?

Platforms have the potential to accept multiple payment providers.
Having userCanPay return readiness results for multiple payment configurations and providers at once, avoids unnecessary drawing magic at build time (eg.: suppose a list of payment buttons –Google, Apple and Microsoft Pay– with dividers of 15 of height, if a payment button is not available, and hence it does not draw itself, the upper and lower dividers overlap, creating a blank space of height 30).

Instead, if the available providers are known at build time, developers can choose what buttons to draw and place them inside of the layout of choice, in a more Flutter-natural and expressive way.

Any alternative ideas @socsieng @jamesblasco @Arkangel12 @domesticmouse?

Right now there is a single method channel that communicates with native code.

On android, canPay returns true if Google Pay is available
On iOS, canPay returns true if Apple Pay Pay is available.

So the result is, if the native wallet is available, both Google Pay and Google Pay are available.

We could:
1. Create a Method channel different for each Wallet and return false in platforms where canPay is not implemented
2. Use one method channel and check the device platform to figure out the wallet.
3. Send the wallet type to the native code, and check if the given wallet is available

In my opinion, the first method is preferred, because we could modularize in packages for different wallets. It would not make sense to check in swift if GooglePay, SamsungPay, or others are supported when we already know.

The second option may work when only using GooglePay for Android and ApplePay for iOs, but it is not scalable, as there are more wallets available and the web supports these two wallets

I am trying to integrate with a payment gateway that requires transactionIdentifier along with paymentData & paymentMethod

Request your support to add it to the Payment Result.

Please find reference below:
https://developer.apple.com/documentation/passkit/pkpaymenttoken/1617003-transactionidentifier

Need to handle the state changes like new subscriptions, renewals, Expirations, and Cancellations to ensure that the state is kept in-sync. Is there documentation explaining how we can achieve that using the "pay" package?

I'm sure to have run pub get multiple times after adding the asset file. But still it says "Unable to load the asset". And I'm not sure what other configurations have I missed.

AFAIK, Both apple and google allows to tweak border radius of the buttons. It would be great to see the buttons having border radius option.

After adding pay to pubspec.yaml, the deployment is failing with below error

pub-cache/hosted/pub.dartlang.org/pay_android-1.0.1/android/src/main/kotlin/io/flutter/plugins/pay_android/GooglePayHandler.kt: (112, 27): Expecting a parameter declaration
pub-cache/hosted/pub.dartlang.org/pay_android-1.0.1/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (37, 28): Expecting a parameter declaration
pub-cache/hosted/pub.dartlang.org/pay_android-1.0.1/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (53, 52): Expecting a parameter declaration
pub-cache/hosted/pub.dartlang.org/pay_android-1.0.1/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (38, 79): Expecting a parameter declaration
pub-cache/hosted/pub.dartlang.org/pay_android-1.0.1/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (52, 67): Expecting a parameter declaration

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':pay_android:compileDebugKotlin'.

The Pay client accepts loading a payment configuration both from an asset stored within the Flutter module, or a JSON string produced at runtime (eg.: loaded from a backend server). This flexibility is not exposed all the way up to the GooglePayButton widget yet.

Include an additional property in the GooglePayButton widget to load the configuration from a JSON string, similar to how the Pay client already offers. Make sure to control for existence of at least one field using assert on the init constructor.

Here is my code

late Pay _payClient = Pay(
[PaymentConfiguration.fromJsonString(convertGPaymentConfigToString())]);

String convertGPaymentConfigToString() {
return jsonEncode({
"provider": "google_pay",
"data": {
"environment": "TEST",
"apiVersion": 2,
"apiVersionMinor": 0,
"allowedPaymentMethods": [
{
"type": "CARD",
"tokenizationSpecification": {
"type": "PAYMENT_GATEWAY",
"parameters": {
"gateway": "example",
"gatewayMerchantId": "gatewayMerchantId"
}
},
"parameters": {
"allowedCardNetworks": ["VISA", "MASTERCARD"],
"allowedAuthMethods": ["PAN_ONLY", "CRYPTOGRAM_3DS"],
"billingAddressRequired": true,
"billingAddressParameters": {
"format": "FULL",
"phoneNumberRequired": true
}
}
}
],
"merchantInfo": {
"merchantId": "01234567890123456789",
"merchantName": "Example Merchant Name"
},
"transactionInfo": {"countryCode": "US", "currencyCode": "USD"}
}
});
}

_payClient.userCanPay(PayProvider.google_pay) returns false
Can anyone tell me what is wrong in code?
@JlUgia

final res = await _payClient.showPaymentSelector(
  provider: Platform.isAndroid ? PayProvider.google_pay : PayProvider.apple_pay,
  paymentItems: [
    PaymentItem(
        amount: amount.toString(),
        label: description,
        status: PaymentItemStatus.final_price,
        type: PaymentItemType.total)
  ],
);
print("After showPaymentSelector:"); // this line is not called!

showPaymentSelector starts payment flow, if user click back button at this stage no return occurs
how to detect this situation?

How do I use the paymentResult to carry out the necessary transactions and send relevant info to my backend ?

Before displaying the Google Pay button, a readiness call is issued to determine whether the user in question can use Google Pay. Most of the times this value does not change. In some situations, the user may leave the app to configure Google Pay and come back once ready, and expect the button to show this time.

Observe on the WidgetsBindingObserver class to issue the readiness Future again when the user brings the app back to the foreground (on resumed)

When trying to initiate a payment flow via a button, the payment immediately crashes, with no output to the console about what went wrong.

The brand guidelines of the button encourage developers to remove the button altogether if the paying with the provider in question is not supported or unavailable. The property childOnError offers implementers a chance to decide what UI to show in case the button can't be displayed.

Come up with a more intuitive name that conveys not only error, but also successful, yet unavailable responses.
Ideas:

• replacement
• childIfUnavailable

Launching lib\main.dart on sdk gphone x86 arm in debug mode...
lib\main.dart:1
e: C:\Users\faheem\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\pay_android-1.0.1\android\src\main\kotlin\io\flutter\plugins\pay_android\GooglePayHandler.kt: (112, 27): Expecting a parameter declaration
e: C:\Users\faheem\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\pay_android-1.0.1\android\src\main\kotlin\io\flutter\plugins\pay_android\PayMethodCallHandler.kt: (37, 28): Expecting a parameter declaration
e: C:\Users\faheem\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\pay_android-1.0.1\android\src\main\kotlin\io\flutter\plugins\pay_android\PayMethodCallHandler.kt: (53, 52): Expecting a parameter declaration

e: C:\Users\faheem\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\pay_android-1.0.1\android\src\main\kotlin\io\flutter\plugins\pay_android\PayPlugin.kt: (38, 79): Expecting a parameter declaration
e: C:\Users\faheem\AppData\Local\Pub\Cache\hosted\pub.dartlang.org\pay_android-1.0.1\android\src\main\kotlin\io\flutter\plugins\pay_android\PayPlugin.kt: (52, 67): Expecting a parameter declaration

FAILURE: Build failed with an exception.

The intention of this plugin is to support as many payment providers as it's useful to developers. Each provider offers diverse forms of presenting information to return results and errors back to the caller, with JSON being a common format.

Let's evaluate how developers typically interact with this information and offer typed structures for those elements or pieces of information that are handled and processed programmatically (eg.: result/error class, display items, etc) and default to a more generic format for chunks of information (eg.: JSON) that are relied to other systems (eg.: backend, PSP).

I am facing native crash when I am trying to make a payment using google pay and stripe as tokenizer. The error I get is

E/MethodChannel#plugins.flutter.io/pay_channel: Failed to handle method call
    java.lang.NullPointerException: Attempt to invoke virtual method 'org.json.JSONObject org.json.JSONObject.putOpt(java.lang.String, java.lang.Object)' on a null object reference
        at io.flutter.plugins.pay_android.GooglePayHandler$Companion.buildPaymentProfile(GooglePayHandler.kt:53)
        at io.flutter.plugins.pay_android.GooglePayHandler.loadPaymentData(GooglePayHandler.kt:98)
        at io.flutter.plugins.pay_android.PayMethodCallHandler.onMethodCall(PayMethodCallHandler.kt:66)
        at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:233)
        at io.flutter.embedding.engine.dart.DartMessenger.handleMessageFromDart(DartMessenger.java:85)
        at io.flutter.embedding.engine.FlutterJNI.handlePlatformMessage(FlutterJNI.java:818)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:336)
        at android.os.Looper.loop(Looper.java:174)
        at android.app.ActivityThread.main(ActivityThread.java:7682)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:516)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:950)

Seems when we actually try to make a payment, there is no transactionInfo object on the payment profile where as

Use the format section in the Flutter style guide as a default strategy to format files in the repository, unless there is supporting rationale that improves readability, comprehension or grouping of core functionality.

When Android applications using the plugin need to include their own native ends, there's a requirement for them to use at least the same minSdkVersion and ext.kotlin.version as the Android side in the plugin.

Confirm this scenario and add explicit guidance in the documentation.
Related to #29.

@domesticmouse, I've seen this issue in other packages as well, are you able to confirm whether this is known and accurate?

How cam I check if Apple Pay or Google Pay has just a card registered and ready to use ? And there is a way to send user to add card to those payment app?

I've just started using the Pay package for my Flutter application. And am facing this issue.

Please help me resolve the issue.

version 1.0.5

E/flutter (26185): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: PlatformException(10, 10: , null, null)
E/flutter (26185): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:597:7)
E/flutter (26185): #1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:158:18)
E/flutter (26185):
E/flutter (26185): #2 PayMethodChannel.userCanPay (package:pay_platform_interface/pay_channel.dart:48:12)
E/flutter (26185):

This issue captures the main characteristics of adding support for payments on iOS through Apple Pay. This is intended as a design foundation (and a discussion if applicable).

Plugin principles:

• It supports multiple payment options within a single platform (if available).
• Idiomatic, useful and unsurprising (it uses strict code style guidelines for the languages used).
• Testable automatically, and released shortly after changes are added and stabilized.
• Built on top of modern and stable technology (Flutter 2, Dart 2.12, Swift, Kotlin, federation).
• Simplicity over flexibility (with alternative integration paths for further customization).
• Open and supporting as many configurations as possible (PSPs, native features).

Apple Pay integration breakdown:

• Use Swift (and follows Swift's API design guidelines).
• Define a JSON-based spec to allow for the creation of exchangeable files that can be loaded once from any source, locally or remotely (use the W3C payment standard spec for Apple Pay as a source for inspiration, except for the display items, which will be added at runtime – see #6).
• Create a raw button that is conceptually separate from the payment logic.

Discussions / challenges

• To maximize the flexibility of mixing and matching federated plugins, the intention is to separate Android and iOS into separate folders/sub-plugins.
• If using the raw assets from Apple Pay to draw the button on the Flutter end is not an option, use a PlatformView to surface the programatic button all the way to the Flutter tree.
• Verify the required steps to use the token returned against public endpoints for different PSPs.
• Supporting dynamic price updates will likely require an additional call to the method channel. Consider deferring this functionality to later versions of the library.

Please do feel free to add to this.
Let's use this overarching foundation to plan the addition of Apple Pay, and potential breakdown of the effort.

Right now both PKPaymentButtonType and PKPaymentNetwork support all versions without conditional macro versions (@available). We should add them to allow lower the minimum version of iOS to match the ones supported by Flutter.

The GooglePayButton widget receives payment configuration through a conceptually immutable parameter: it's recommended that the same configuration that checks whether a user is ready to pay is used to perform the actual payment.

Consider the following:

• Document the behavior of intentionally not updating the confguration if ia different asset or JSON string is added.
• Reject changes to the payment configuration through intentional exceptions or errors

In our case, we don't need users CONTACT and SHIPPING information.
We would like to have the ability to make them hidden/not required during payment.

I've tried to remove requiredShippingContactFields & requiredBillingContactFields fields from default_payment_profile_apple_pay.json but they are still required

We need support for Google pay in Apple devices.
There are countries where Apple pay isn't supported and people use Google pay instead extensively
Especially in countries like India where Google pay is goto payment interface in both android and Apple users than the app provided by the Indian government for UPI transactions

And Google pay is the leading UPI provider in India contributing for more than 50% of the transactions in the country

Hey I am new at Payment in flutter and I have some simple questions, I am searching for a payment method for a service app (like uber or food delivery).

1. Can I use this package to implement this kind of payment (service/ product payment) ?

2. Where I add my billing information for apple and google?

For example in Stripe I have an account with my own api where I add my billing information and check payment status and analytics

3. After I have configured the app and all the merchantID etc... When and how Apple an google will send my user payments?

4. Is there a tax like for in app purchase?

Thank you so much.

Seems simple things but I think should be added to package description to help distribute the usage of this package to new adopter like me :)

The app is working fine in simulator with simulated card but when i running same code in physical devices, then userCanPay(PayProvider.apple_pay) always retruning false.

We need to support dynamic configurations with different countries and currencies, based on in-app-content.

Also, we can't rely on the press-and-pay native-buttons of this plugin, since we sometimes need the payment to start after using another unrelated button. This worked with the now discontinued stripe_payment.

1. How can I start native payment from code, not button?

2. How can I feed the pay-client with a custom configuration that is not stored as an asset?

What do you think about updating the dependencies to work with dart 2.12 and Flutter 2?

I think that once this is released, it should be supported in the latest released version.

Migrating the packages to null safety should be straightforward. I am happy to help and submit a PR once the current one is merged 👍

The sooner we migrate, the lesser changes we will need to do.

I've placed a GooglePayButton but it does not show. Enabling debug paint, you can see that it is very tiny. Setting height and width parameters also do not help.

I get these errors:

E/flutter (14723): #1      _AssertionError._throwNew (dart:core-patch/errors_patch.dart:36:5)
E/flutter (14723): #2      new PaymentConfiguration._ (package:pay_platform_interface/core/payment_configuration.dart:55:16)
E/flutter (14723): #3      PaymentConfiguration.fromAsset (package:pay_platform_interface/core/payment_configuration.dart:85:33)
E/flutter (14723): <asynchronous suspension>
E/flutter (14723): #4      Future.wait.<anonymous closure> (dart:async/future.dart)
E/flutter (14723): <asynchronous suspension>
E/flutter (14723): #5      Pay._loadConfigAssets (package:pay/src/pay.dart:45:25)
E/flutter (14723): <asynchronous suspension>
E/flutter (14723): 

Hi,

I am getting this weird issue when building:
e: /Applications/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.2/android/src/main/kotlin/io/flutter/plugins/pay_android/GooglePayHandler.kt: (112, 27): Expecting a parameter declaration e: /Applications/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.2/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (37, 28): Expecting a parameter declaration e: /Applications/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.2/android/src/main/kotlin/io/flutter/plugins/pay_android/PayMethodCallHandler.kt: (53, 52): Expecting a parameter declaration e: /Applications/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.2/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (38, 79): Expecting a parameter declaration e: /Applications/flutter/.pub-cache/hosted/pub.dartlang.org/pay_android-1.0.2/android/src/main/kotlin/io/flutter/plugins/pay_android/PayPlugin.kt: (52, 67): Expecting a parameter declaration

Any advice on how to fix it?

There is no token at all. how to understand whether my store setting is working or not?

{
	token: ,
	shippingContact: null,
	paymentMethod: {
		network: null,
		type: 0,
		displayName: SimulatedInstrument
	},
	billingContact: null,
	shippingMethod: null
}

everything seems to work

Setting up jason

My Button

One alternative to configure payment providers for this plugin is to create a configuration file in JSON format, and reference it in the instantiation of the payment client or the widgets directly.

This configuration is not fully specified for all providers.:

• Apple Pay – currently using W3C payment request specification
• Google Pay – based on the existing JSON spec in the SDK

Create a fully specified JSON schema for the parameters, types and values allowed for each provider. The current plan is to use JSON Schema, currently published as a draft IETF tool, and open to other suggestions.

As title explains this is what I am getting after a successful payment from apple pay. I believe token should be in response of the apple pay.

I am getting a WalletMerchantError when making a payment, it's working fine when the environment is set to ##TEST.

WalletMerchantError: Error in loadPaymentData: PaymentDataRequest.allowedPaymentMethods[0].parameters.allowedAuthMethods[0] = MASTERCARD is not a valid enum value for this field.

json

{
    "provider": "google_pay",
    "data": {
        "environment": "PRODUCTION",
        "apiVersion": 2,
        "apiVersionMinor": 0,
        "allowedPaymentMethods": [
            {
                "type": "CARD",
                "tokenizationSpecification": {
                    "type": "PAYMENT_GATEWAY",
                    "parameters": {
                        "gateway": "example",
                        "gatewayMerchantId": "Merchant id form dashboard"
                    }
                },
                "parameters": {
                    "allowedCardNetworks": [
                        "VISA",
                        "MASTERCARD"
                    ],
                    "allowedAuthMethods": [
                        "MASTERCARD",
                        "VISA"
                    ],
                    "billingAddressRequired": false,
                    "billingAddressParameters": {
                        "format": "FULL",
                        "phoneNumberRequired": true
                    }
                }
            }
        ],
        "merchantInfo": {
            "merchantId": "Merchant id form dashboard",
            "merchantName": "Merchant Name"
        },
        "transactionInfo": {
            "countryCode": "US",
            "currencyCode": "USD"
        }
    }
}

code

 void makePayment() async {
    Pay _payClient = Pay.withAssets([
      'default_payment_profile_google_pay.json',
    ]);

    final _paymentItems = [
      PaymentItem(
        label: 'Total',
        amount: '100',
        status: PaymentItemStatus.final_price,
      )
    ];

    try {
      final result = await _payClient.showPaymentSelector(
        provider: PayProvider.google_pay,
        paymentItems: _paymentItems,
      );
      print(result.toString());
    } catch (e) {
      ScaffoldMessenger.of(context)
          .showSnackBar(SnackBar(content: Text('An error occourred')));
    }
  }

EDIT:
Tried removing master cart from the json array and reinstalled the app but now it show
c07-16 18:20:14.125 22243 22243 W WalletMerchantError: Error in loadPaymentData: PaymentDataRequest.allowedPaymentMethods[0].parameters.allowedAuthMethods[0] = VISA is not a valid enum value for this field.

Like we have option for card, how can I enable support for UPI payments?