This is an addon of "Easy Digital Downloads" plugin.
If you want to make discount code as a required field, this plugin will help.
During checkout when a customer will try to purchase without entering any discount code, checkout process will be interrupted and customer will see an error notice.
You can configure the error notice text from "Downloads>Force Discount" menu from admin panel.
From your WordPress dashboard
- Visit 'Plugins > Add New'
- Search for 'Force Discount for EDD'
- Activate 'Force Discount for EDD' from your Plugins page.
From
WordPress.org
- Download 'Force Discount for EDD'.
- Upload the 'edd-force-discount' folder to your '/wp-content/plugins/' directory, using your favorite method (ftp, sftp, scp, etc...)
- Activate 'Force Discount for EDD' from your Plugins page.
After that you can configure the plugin settings from "Downloads>Force Discount" menu from admin panel.