When you're trying to activate Office 2016 for Mac, you might receive this error:
Installation limit reached
Your account <email address> has been used to activate Office on the maximum number of computers allowed. Visit your account page to manage your settings and then return here to retry activation.
This error occurs when you've reached the maximum number of activations that your Office 365 subscription allows.
Office 365 Home or Personal
To activate Office on this Mac, you'll need to go to your account page to deactivate an existing Office 365 install, and then try to activate again.
Office 365 for business
Sign in to the Office 365 portal.
Go to Settings > Office 365 > Software.
Under Manage installs, review the list of computers, and choose Deactivate next to one you no longer need and try to activate again.
If you're still having issues with activating Office 2016 for Mac, please contact Microsoft support.