Invitation Codes: Gravityforms Add-on

This plugin is created to enable WordPress site owners to specify a custom invitation code to be used with Gravity Forms.
Once an invitation code is specified on a form, the user can’t submit that form until that invitation code is entered in
the field during the form submission. This plugin can be combined with the Gravity Forms User Registration Add-On to make
sure that only people with a correct invitation code can register on your website.