https://getawesomesupport.com/addons/envato-validation/

We’ve got you covered. With the Envato Validation addon, you can limit tickets submissions to your actual clients. By asking for their Envato purchase code, the plugin will make sure that the people asking you for help did buy your product.

The plugin is really flexible and has more advanced features than what you usually find in this kind of tool. Here is what really makes it better.