Problem switching from one Mac to another with Parallels Desktop Standard Edition 18

Hello, I have two Parallels licenses. When I try to activate the app on a new Mac, on one it says, "This license has exceeded its activation limit and can no longer be used to activate new copies of the product." On the other, it says, "To activate Parallels Desktop 18, you must update this license key. It will not activate the current version because it was created for previous versions of Parallels Desktop."
I don't even think I can upgrade to newer versions because I need to use older programs on Windows 7.
Can you remove the restriction?