Kowsar Hossain

If you want to make coupon code as a required field, this plugin will help.
During checkout when a customer will try to place an order without entering any coupon code, checkout process will be interrupted and customer will see an error notice.
You can configure the error notice text from “WooCommerce>Force Coupon” menu from admin panel.

Force Coupon for WooCommerce

A lightweight WooCommerce based plugin to force the customer to enter a coupon code during checkout

gilbarbara

Once activated and configured, this plugin will require users to fill selected fields before publishing posts, page, custom post types / custom fields.

Requird

Require users to fill selected fields before posting.

Force Coupon for WooCommerce vs Requird