ProductAddons ID not saved/retrieved correctly

The Addons ID is stored as “product_addon_id“ but retrieved as “product_addon_id_“ which causes the ID to be empty and because of it, it gets stored with a new ID each time the product is updated.

Changing the line 893 in file “woocommerce-appointments/includes/integrations/woocommerce-product-addons/includes/admin/class-wc-product-addons-admin.php“ fixes it.