This usually happens if the purchase code was previously used on another domain, even if that installation has been deleted. To resolve this:
Contact the support team and provide your purchase code.
Specify the old domain and the new domain where you want to activate the code.
The support team will reset or release the purchase code.
Once reset, you can activate the code on the new domain without issues.
Tip: Always deactivate or remove the previous installation before moving to a new domain to avoid validation conflicts.