Thanks for writing in!
To validate the theme properly, please do the following:
1] Please login to your account and assign the license (https://theme.co/apex/licenses). You need to assign the license to your site using this url: https://www.example.com/. You have to make sure that url you just assign is the same as the one you have in your settings, https://theme.co/apex/licenses
2] Go back to Pro > Validation again, and insert the license code.
You can only use the license code to validate Pro theme when the license code is already assigned to the site URL. It will give you the error when you try to use the license code that is assigned to another domain url.
And please review the changes that we made on how you are going to validated your X theme because we made a big change in the process. Please check it out here: https://theme.co/apex/forum/t/setup-product-validation/55