@VisibleForTesting
    @NonNull
    static String getDeleteCustomerSourceUrl(@NonNull String customerId, @NonNull String sourceId) {
        return getApiUrl("customers/%s/sources/%s", customerId, sourceId);
    }
@ VisibleForTesting @ NonNull static String getDeleteCustomerSourceUrl ( @ NonNull String customerId , @ NonNull String sourceId ) { return getApiUrl ( "customers/%s/sources/%s" , customerId , sourceId ) ; }
@return https://api.stripe.com/v1/customers/:customer_id/sources/:source_id