The validation failed because you assigned the license to a domain yet your staging site has a different url. To validate X properly, please do the following:
1] Please login to your account and assign the license. 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 > Validate again, and insert the license code.
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
It is now validated because I have assigned your staging site to the license code. Please check your licenses page: https://theme.co/apex/licenses