When you start Parallels Desktop for Mac it will prompt you to sign in to your Parallels account. Skip this step and click on the Business Edition button at the bottom left corner of the window instead.
Enter your activation key (dashes will be added automatically).
Once you enter the key, it will be validated. If the key is valid, it will be marked with a check mark.
Note: An Internet connection is required for activation of Parallels Desktop Business Edition.
If the key is not valid, it will be marked with a red cross sign. Check to see if you entered the key correctly.
If the key has been successfully validated, click Activate.
If your Mac is connected to the Internet, Parallels Desktop Business Edition will be successfully activated.