request_payment.kt

val request = IsReadyToPayRequest.fromJson(isReadyToPayRequest.toString())
request?.let {
    val task = paymentsClient?.isReadyToPay(request)
    task?.addOnCompleteListener { completedTask ->
        val result = completedTask.getResult(ApiException::class.java)
        result?.let {
            button_google_pay.setOnClickListener { view -> requestPayment(view) }
            button_google_pay.visibility = View.VISIBLE
        }
    }
}