Thanks for writing in!
Kindly check if you got the correct license key into your site admin. For your convenience: https://theme.co/apex/licenses
Also, please make sure you've added the correct URL in your licenses page. Here's an article to guide you with the validating your product:
You can scan this in case you've just missed some steps.
Please try going to your license page, https://theme.co/apex/licenses and make sure the purchase key is assigned to that given domain. Or do you mean you were revoking it from your site admin? You still need to remove the assigned site to your purchase key and it should be doable in your license page. Afterwards, re-assign your preferred site then do the validation in your site's admin.
I advised you create a separate thread next time so as we can focus catering your support needs there. This is also so we can avoid confusion on replies.