ECE: fix missing product ID when adding product with variations (#3880)

* Fix missing product ID when adding product with variations

* Add changelog and readme entries

Author: annemirasol

changelog.txt

@@ -1,6 +1,7 @@
 *** Changelog ***
 
 = 9.2.0 - xxxx-xx-xx =
+* Fix - Fix missing product_id parameter for the express checkout add-to-cart operation.
 * Fix - Fix the quantity parameter for the express checkout add-to-cart API call.
 * Dev - Replaces part of the StoreAPI call code for the cart endpoints to use the newly introduced filter.
 * Fix - Clear cart first when using express checkout inside the product page.

client/entrypoints/express-checkout/index.js

@@ -610,6 +610,13 @@ jQuery( function ( $ ) {
 				qty: $( quantityInputSelector ).val(),
 			};
 
+			// Check if product is a variable product.
+			if ( $( '.single_variation_wrap' ).length ) {
+				productId = $( '.single_variation_wrap' )
+					.find( 'input[name="product_id"]' )
+					.val();
+			}
+
 			if ( $( '.wc-bookings-booking-form' ).length ) {
 				productId = $( '.wc-booking-product-id' ).val();
 			}

readme.txt

@@ -111,6 +111,7 @@ If you get stuck, you can ask for help in the [Plugin Forum](https://wordpress.o
 == Changelog ==
 
 = 9.2.0 - xxxx-xx-xx =
+* Fix - Fix missing product_id parameter for the express checkout add-to-cart operation.
 * Fix - Fix the quantity parameter for the express checkout add-to-cart API call.
 * Dev - Replaces part of the StoreAPI call code for the cart endpoints to use the newly introduced filter.
 * Fix - Clear cart first when using express checkout inside the product page.