After the RestroFood plugin has been activated, it is not possible to enter a coupon code on the checkout page. We’ve tried also with default WP themes.
We are sorry to say that the default checkout page’s coupon system will not work if you are using RestroFood. You must have to use RestroFood’s Cart and Checkout system. That will work without having an issue https://prnt.sc/N7aRagPpOTPA