Binaries were built against Android `9.0` with NDK `r19`.
They are not supported by older Android versions. Either upgrade your device or compile it by yourself using provided _Dockerfile_.
Please follow _Download_ section for more details.
> Compiled iperf and iperf3 binaries using SDK 4333796 and NDK r19 for devices with Android 9.0+ (API level 28+)