Computer Configuration > Administrative Templates > Microsoft Office 2016 (Machine) > Volume Activation
Machine
HKLM\software\policies\microsoft\officesoftwareprotectionplatform
This policy setting allows you to prevent the Token Activation prompt for activation dialog from closing. If you enable this policy setting, the "Close" button and the "X" button at the upper right of the dialog are suppressed. If the user proceeds with activation and fails, the buttons will be enabled the next time the dialog appears. If you disable or do not configure this policy setting, the user may close the dialog when prompted for activation.