Licensing & payments · Activating your licence
How do I activate on a Mac that doesn't have my email on it?
Short answer: Read the License Code from the email on any device, then type your purchase email and the code into Settings → License on the Mac and click Activate.
Type the code in by hand. Every activation email includes the License Code as well as the button, so read it on your phone or another computer, then on the Mac open Settings → License, enter your purchase email and the code, and click Activate.
The button only activates the Mac you click it on, so the manual route is the one to use for a different Mac.