After creating list and adding keywords to list, you still need to apply list to WPForms form field.
Before apply invitation codes list to a form field you need enable BSK Blacklist on form settings page.
Focus on the field you'd like to apply list to on WPForms form edit page
You will see the BSK Blacklist section in Advanced Options tab.
You may customize the validation message for field, if you leave it blank then the validation message will use what you set in form settings page.
For "Select comparison..." dropdown, it is the way how to check the field value match a field. If includes same or contain( field value contain keyword in list ) with case-insensitive or not.
Purchase BSK Forms Blacklist Pro