MacOS error message "Another account from your organisation is already signed in on"

Hi @Siddharth Nayak
Thank you for posting question to Microsoft Q&A Forum.

According to this issue, please follow this article to download Microsoft License Removal Tool then use to clear the existing credentials from your Mac then try to sign-in again.

If the issue still persists, please search for the application name "Terminal" and run this command:

defaults write com.microsoft.Word ResetOneAuthCreds -bool YES

You could replace Word with Excel, PowerPoint or Outlook based on the application you encountered this error message.

I hope this information is helpful, please let me know if you have any further questions.

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Try this: Sign out of all Office apps, use the Microsoft License Removal Tool to clear cached credentials, and then restart your Mac. After restarting your Mac and reinstalling the latest version of Office, sign in to resolve the cached credentials and account sync errors.