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 Office allows. With a one-time purchase of Office for Mac, you only get one install.
One-time purchase or HUP install
If you bought a one-time purchase of Office for Mac or received it through the Home Use Program, you're allowed only one install of Officefor Mac and you can't deactivate it in the same way you may do an Office 365 license. If you need to switch your copy of Office to a different Mac, you can do so over the phone. Contact Microsoft support.