diff -u b/modules/payment/src/PluginForm/PaymentMethodOffsiteAddForm.php b/modules/payment/src/PluginForm/PaymentMethodOffsiteAddForm.php
--- b/modules/payment/src/PluginForm/PaymentMethodOffsiteAddForm.php
+++ b/modules/payment/src/PluginForm/PaymentMethodOffsiteAddForm.php
@@ -93,7 +93,7 @@
    */
   public static function processRedirectForm(array $form, FormStateInterface $form_state, array &$complete_form) {
     $complete_form['#action'] = $form['#redirect_url'];
-    $complete_form['#attributes']['class'][] = 'payment-redirect-form';
+    $complete_form['#attributes']['class'][] = 'payment-redirect-me';
     // The form actions are hidden by default, but needed in this case.
     $complete_form['actions']['#access'] = TRUE;
     foreach (Element::children($complete_form['actions']) as $element_name) {
diff -u b/modules/payment/src/PluginForm/PaymentOffsiteForm.php b/modules/payment/src/PluginForm/PaymentOffsiteForm.php
--- b/modules/payment/src/PluginForm/PaymentOffsiteForm.php
+++ b/modules/payment/src/PluginForm/PaymentOffsiteForm.php
@@ -104,7 +104,7 @@
    */
   public static function processRedirectForm(array $form, FormStateInterface $form_state, array &$complete_form) {
     $complete_form['#action'] = $form['#redirect_url'];
-    $complete_form['#attributes']['class'][] = 'payment-redirect-form';
+    $complete_form['#attributes']['class'][] = 'payment-redirect-me';
     // The form actions are hidden by default, but needed in this case.
     $complete_form['actions']['#access'] = TRUE;
     foreach (Element::children($complete_form['actions']) as $element_name) {
diff -u b/modules/payment_example/src/Controller/DummyRedirectController.php b/modules/payment_example/src/Controller/DummyRedirectController.php
--- b/modules/payment_example/src/Controller/DummyRedirectController.php
+++ b/modules/payment_example/src/Controller/DummyRedirectController.php
@@ -49,7 +49,7 @@
     $total = $this->currentRequest->request->get('total');
 
     if ($total > 20) {
-      return new TrustedRedirectResponse($return . '?' . $this->buildQuery());
+      return new TrustedRedirectResponse($return);
     }
 
     return new TrustedRedirectResponse($cancel);
@@ -86,7 +86,7 @@
     $total = $this->currentRequest->query->get('total');
 
     if ($total > 20) {
-      return new TrustedRedirectResponse($return . '?' . $this->buildQuery());
+      return new TrustedRedirectResponse($return);
     }
 
     return new TrustedRedirectResponse($cancel);