Verify the structure of STX token transfer payload about ledger-stacks

[neithanmo]

Did not realize it was a previous commit. Thank you, It clarifies a lot.

[kantai]

Is this field optional? if so, there is a byte that indicates whether this value is present or not?

No -- the memo field is always present in the transaction.

[0, 5, (1-byte addrs version, Hash160), ...]

The first byte indicates that the payload is a token transfer. The only native token transfer operation is a STX token transfer. The second byte is part of the serialization of the recipient address -- 0x05 indicates that it is a "standard recipient", 0x06 indicates a "contract recipient". See the documentation here: https://github.com/blockstack/stacks-blockchain/blob/master/sip/sip-005-blocks-and-transactions.md#transaction-payloads-1, which was updated in April (the link you provided is an old commit).