anchor.diff:  
           public void CheckoutWithNativeWebView(CheckoutSuccessCallback success, CheckoutCancelCallback cancelled, CheckoutFailureCallback failure) {
               if (WebCheckout == null) {
  -                // TODO use custom exception
  -                throw new Exception("This platform does not support checkout with web pay");
  +                throw new PlatformNotSupportedException("This platform does not support checkout with web pay");
               }
   
               GetWebCheckoutLink(url => {
  
positive.code: 
          public void CheckoutWithNativePay(string key, CheckoutSuccessCallback success, CheckoutCancelCallback cancelled, CheckoutFailureCallback failure) {
              if (NativeCheckout == null) {
                  // TODO use custom exception
                  throw new Exception("This platform does not support checkout with native pay");
              }
  
              CheckoutSave(error => {
  
negative.code:             if (NativeCheckout != null) {
                  NativeCheckout.ShowPaymentSetup();
              } else {
                  throw new PlatformNotSupportedException("This platform does not support showing a native payment setup");
              }
          }
  
  