diff --git a/modules/ppcp-button/src/Endpoint/AbstractCartEndpoint.php b/modules/ppcp-button/src/Endpoint/AbstractCartEndpoint.php
index d74d59c55..3133cf544 100644
--- a/modules/ppcp-button/src/Endpoint/AbstractCartEndpoint.php
+++ b/modules/ppcp-button/src/Endpoint/AbstractCartEndpoint.php
@@ -153,9 +153,10 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 	/**
 	 * Handles errors.
 	 *
+	 * @param bool $send_response If this error handling should return the response.
 	 * @return void
 	 */
-	private function handle_error(): void {
+	protected function handle_error( bool $send_response = true ): void {
 
 		$message = __(
 			'Something went wrong. Action aborted',
@@ -173,14 +174,16 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 			wc_clear_notices();
 		}
 
-		wp_send_json_error(
-			array(
-				'name'    => '',
-				'message' => $message,
-				'code'    => 0,
-				'details' => array(),
-			)
-		);
+		if ( $send_response ) {
+			wp_send_json_error(
+				array(
+					'name'    => '',
+					'message' => $message,
+					'code'    => 0,
+					'details' => array(),
+				)
+			);
+		}
 	}
 
 	/**
@@ -259,7 +262,9 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 	private function add_product( \WC_Product $product, int $quantity ): bool {
 		$cart_item_key = $this->cart->add_to_cart( $product->get_id(), $quantity );
 
-		$this->cart_item_keys[] = $cart_item_key;
+		if ( $cart_item_key ) {
+			$this->cart_item_keys[] = $cart_item_key;
+		}
 		return false !== $cart_item_key;
 	}
 
@@ -294,7 +299,9 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 			$variations
 		);
 
-		$this->cart_item_keys[] = $cart_item_key;
+		if ( $cart_item_key ) {
+			$this->cart_item_keys[] = $cart_item_key;
+		}
 		return false !== $cart_item_key;
 	}
 
@@ -322,7 +329,9 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 
 		$cart_item_key = $this->cart->add_to_cart( $product->get_id(), 1, 0, array(), $cart_item_data );
 
-		$this->cart_item_keys[] = $cart_item_key;
+		if ( $cart_item_key ) {
+			$this->cart_item_keys[] = $cart_item_key;
+		}
 		return false !== $cart_item_key;
 	}
 
@@ -333,6 +342,9 @@ abstract class AbstractCartEndpoint implements EndpointInterface {
 	 */
 	protected function remove_cart_items(): void {
 		foreach ( $this->cart_item_keys as $cart_item_key ) {
+			if ( ! $cart_item_key ) {
+				continue;
+			}
 			$this->cart->remove_cart_item( $cart_item_key );
 		}
 	}
diff --git a/modules/ppcp-button/src/Endpoint/SimulateCartEndpoint.php b/modules/ppcp-button/src/Endpoint/SimulateCartEndpoint.php
index 5e3796dbb..ead2f4229 100644
--- a/modules/ppcp-button/src/Endpoint/SimulateCartEndpoint.php
+++ b/modules/ppcp-button/src/Endpoint/SimulateCartEndpoint.php
@@ -27,6 +27,13 @@ class SimulateCartEndpoint extends AbstractCartEndpoint {
 	 */
 	private $smart_button;
 
+	/**
+	 * The WooCommerce real active cart.
+	 *
+	 * @var \WC_Cart|null
+	 */
+	private $real_cart = null;
+
 	/**
 	 * ChangeCartEndpoint constructor.
 	 *
@@ -65,24 +72,14 @@ class SimulateCartEndpoint extends AbstractCartEndpoint {
 			return false;
 		}
 
-		// Set WC default cart as the clone.
-		// Store a reference to the real cart.
-		$active_cart = WC()->cart;
-		WC()->cart   = $this->cart;
+		$this->replace_real_cart();
 
-		if ( ! $this->add_products( $products ) ) {
-			return false;
-		}
+		$this->add_products( $products );
 
 		$this->cart->calculate_totals();
 		$total = (float) $this->cart->get_total( 'numeric' );
 
-		// Remove from cart because some plugins reserve resources internally when adding to cart.
-		$this->remove_cart_items();
-
-		// Restore cart and unset cart clone.
-		WC()->cart = $active_cart;
-		unset( $this->cart );
+		$this->restore_real_cart();
 
 		// Process filters.
 		$pay_later_enabled           = true;
@@ -119,4 +116,44 @@ class SimulateCartEndpoint extends AbstractCartEndpoint {
 		return true;
 	}
 
+	/**
+	 * Handles errors.
+	 *
+	 * @param bool $send_response If this error handling should return the response.
+	 * @return void
+	 *
+	 * phpcs:disable Generic.CodeAnalysis.UselessOverridingMethod.Found
+	 */
+	protected function handle_error( bool $send_response = false ): void {
+		parent::handle_error( $send_response );
+	}
+
+	/**
+	 * Replaces the real cart with the clone.
+	 *
+	 * @return void
+	 */
+	private function replace_real_cart() {
+		// Set WC default cart as the clone.
+		// Store a reference to the real cart.
+		$this->real_cart = WC()->cart;
+		WC()->cart       = $this->cart;
+	}
+
+	/**
+	 * Restores the real cart.
+	 *
+	 * @return void
+	 */
+	private function restore_real_cart() {
+		// Remove from cart because some plugins reserve resources internally when adding to cart.
+		$this->remove_cart_items();
+
+		// Restore cart and unset cart clone.
+		if ( null !== $this->real_cart ) {
+			WC()->cart = $this->real_cart;
+		}
+		unset( $this->cart );
+	}
+
 }