After creating list and adding keywords to list, you still need to apply list to Gravity Forms form field.
Open Advanced tab of the field you'd like to apply list to on Gravity forms form edit page
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.
Update Gravity Forms form to save what you set to the field.Purchase Gravity Forms Blacklist Pro