Proposed explanation and solutions for Office C2R 'Your license isn't genuine' banner:

Solution:

If you are seeing this banner on Office apps, the below activators can resolve it.

• Use the latest KMS_VL_ALL (Mirror) or MAS to activate Office
• Done.

Alternate Solution:

• Change the Office C2R update channel to Production::MEC | MonthlyEnterprise
  To do that, open the command prompt as admin and enter below lines and press enter,

  reg add HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Configuration /v CDNBaseUrl /t REG_SZ /d "http://officecdn.microsoft.com/pr/55336B82-A18D-4DD6-B5F6-9E5095C314A6" /f
  reg delete HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Configuration /v UpdateUrl /f
  reg delete HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Configuration /v UpdateToVersion /f
  reg delete HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Updates /v UpdateToVersion /f
  reg delete HKLM\SOFTWARE\Policies\Microsoft\Office\16.0\Common\OfficeUpdate\ /f
  "%CommonProgramFiles%\microsoft shared\ClickToRun\OfficeC2RClient.exe" /update user

  Make sure the Internet is connected and Office is successfully updated with the last command.
  Source, thanks to @abbodi1406
  Thanks to @Teknik for the idea of changing the update channel.
   

P.S.

• If you have any conflicting info or any other useful info regarding this then please email me at windowsaddict@protonmail.com

Updated on 10-Jan-2022