Thank you for the details. I have checked your APEX account and I see that you have two licenses. The licenses were already assigned to the site urls. Please be advised that you can only validate the site url that is assigned to the license codes.
To validate X 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, Settings > General > Site Address
2] Go back to X > Validation, and insert the license code.
And please review the changes that we made on how you are going to validate 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
Hope this helps.