Custom Coupons M2 - Setting Error Messages for Entire Store
Setting error messages for the Entire Store
The site admin can decide to set Custom Error Messages for coupons applied to any product on the store as well as on an individual Basis. This is obviously a lot quicker. Any individual price rules that are applied will override the global settings explained here too so this doesn't completely remove the fine tuning that you may do with your error messages if you so choose.
To set site wide custom error messages, from the admin panel navigate to Stores → Configuration → Sales → Custom Coupons Error Messages.
Below the toggle to enable / disable the module are fields for entering Messages that will appear to customers when different errors occur for coupons at checkout.
For each error, enter a message that you would like to display to customers.
Then to save your changes click on the Save Config button above and to the right of the Configuration Settings.