LaunchActivity.kt

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        PaymentConfiguration.init("my_key")
        CustomerSession.initCustomerSession(MyEphemeralKeyProvider())
      ...
    }

MyEphemeralKeyProvider.kt

class MyEphemeralKeyProvider(val context: Context): EphemeralKeyProvider {

    override fun createEphemeralKey(apiVersion: String,
                                    keyUpdateListener: EphemeralKeyUpdateListener) {

      //my api call
        PaymentApi.create().getEphemeralKey()
                .enqueue {
                    when(this) {
                        is Result.Success -> {
                            keyUpdateListener.onKeyUpdate(data.string())
                        }
                        is Result.Error -> //error
                    }
                }
    }
}

SomeOtherActivit.kt

    //none of the CustomerRetrievalListener methods called if getting ephemeral key failed. so my progress never hides itself
    //I want to learn if there is a way to check ephemeral key is available. if not i will not start retreiving customer
    //or should I run CustomerSession.initCustomerSession(MyEphemeralKeyProvider()) before every CustomerSession methods
    
    showProgress()
    CustomerSession.getInstance().retrieveCurrentCustomer(object : CustomerSession.CustomerRetrievalListener {
            override fun onCustomerRetrieved(customer: Customer) {
                recyclerView.adapter = PaymentAdapter(customer.sources)
                hideProgress()
            }

            override fun onError(errorCode: Int, errorMessage: String?) {
                hideProgress()
                toast("Error retrieving payment methods")
            }
        })