ActivityOrFragment.kt

class MainActivity : AppCompactActivity() {
     
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    MpesaSdk.pay(
            amount = "20.0",
            transactionReference = "transactin_reference",
            activity = this, // Actvity
            onPaymentComplete =  {
                if(it == null) {
                    // payment was not successful (Eg: Show error message on your app)
                }
                else {
                    // payment was successful do what ever you need (Eg: Show success message)
                    it.conversationId
                    it.transactionId
                }
            }
        )
}

App.kt

class App : Application(){

    companion object {
        private val debugShortCode = "debug_short_code"
        private val mpesaShortCode = "production_short_code"

        private const val mPesaApiKey = "mpesa_prod_api_key"
        private const val debugApiKey = "mpesa_debug_api_key"

        private const val debugPublicKey = """mpesa_debug_public_key"""
        private const val mPesaPublicKey = """mpesa_production_public_key"""
    }
    
    override fun onCreate() {
        super.onCreate()
        setupMpesaSdk()
    }

    private fun setupMpesaSdk() {
        MpesaSdk.init(
            apiKey = if (Features.SandboxMpesa.isEnabled) debugApiKey else mPesaApiKey,
            publicKey = if (Features.SandboxMpesa.isEnabled) debugPublicKey else mPesaPublicKey,
            serviceProviderCode = if (Features.SandboxMpesa.isEnabled) debugShortCode else mpesaShortCode,
            serviceProviderName = "Ruca", //ruca.co.mz
            endpointUrl = if (Features.SandboxMpesa.isEnabled) MpesaSdk.SANDBOX_BASE_URL else MpesaSdk.PRODUCTION_BASE_URL,
            serviceProviderLogoUrl = "logo_url"
        )
    }
}

Composable.kt

fun RenderContent() {
    var amount by remember {
        mutableStateOf("0")
    }

    var launchPayment by remember {
        mutableStateOf(false)
    }

    val result = remember { mutableStateOf<C2BPaymentSuccess?>(null) }
    val launcher = rememberLauncherForActivityResult(C2BResultContract()) {
        result.value = it
        launchPayment = false
    }

    result.value?.run {
        launchPayment = false
        Toast.makeText(LocalContext.current, "Payment result is: $this", Toast.LENGTH_LONG).show()
    }

    Box(modifier = Modifier.fillMaxSize(), contentAlignment = Alignment.Center) {
        Column(
            modifier = Modifier.padding(16.dp),
            horizontalAlignment = Alignment.CenterHorizontally
        ) {
            OutlinedTextField(
                value = amount,
                onValueChange = {
                    amount = it
                },
                keyboardOptions = KeyboardOptions(keyboardType = KeyboardType.Number),
                label = {
                    Text("Valor a pagar")
                }
            )

            Button(
                modifier = Modifier
                    .padding(16.dp)
                    .fillMaxWidth(),
                onClick = {
                    result.value = null
                    launchPayment = true
                }) {
                Text(modifier = Modifier.padding(8.dp), text = "Pagar com M-pesa")
            }
        }

        if (launchPayment) {
            MpesaSdk.pay(
                amount = amount,
                launcher = launcher,
                transactionReference = UUID.randomUUID().toString().take(6)
            )
        }
    }
}

Features.kt

sealed class Features(val isEnabled: Boolean) {
    object SandboxMpesa : Features(BuildConfig.DEBUG)
}

1. Configure the sdk in the App.kt file.
   PS Don't forget to register your app in the manifest: More info here https://developer.android.com/guide/topics/manifest/manifest-intro
2. Depending on how your app is built use the Composable or Activity example to use the sdk.