Microsoft 365 activation fails with "Unknown Error 0x0" on macOS Big Sur 11.7.11

Question

Dear Microsoft Support,

I am experiencing a persistent activation issue with Microsoft 365 on my Mac.

System information

• MacBook Pro (Retina, 13-inch, Late 2013)
• macOS Big Sur 11.7.11
• Microsoft 365 Personal (active subscription)
• Microsoft account: ******@gmail.com

Problem

Microsoft Word and Excel cannot be activated.

When I choose Already bought Office? Sign in, the applications either:

• immediately display Unknown Error (0x0) before any sign-in page appears,

or

• allow me to enter my email address, but after clicking Next, immediately return:

Unknown Error The error code is: 0x0

The password page never appears.

The same behavior occurs in both Word and Excel.

Subscription status

• Microsoft 365 Personal subscription is active until February 2027.
• I can successfully sign in to:
  • account.microsoft.com
    • office.com
    • The subscription is correctly associated with my Microsoft account.

Troubleshooting already performed

• Completely removed and reinstalled Microsoft Office.
• Tested both Office 16.77 and 16.75.
• Removed Office containers and cache.
• Deleted Microsoft preferences.
• Deleted Group Containers.
• Deleted and recreated Microsoft Registration Database.
• Verified Microsoft Licensing Helper (licensingV2.helper) is running.
• Verified network connectivity.
• Verified HTTPS access to Microsoft authentication servers:
  • https://login.microsoftonline.com (HTTP 200 OK)
  • Verified Safari authentication works normally.
  • Cleared Keychain entries related to Microsoft.
  • Rebooted multiple times.

None of these steps changed the behavior.

Additional observations

• Office successfully reaches the Microsoft authentication service.
• The problem occurs exactly when the application should transition from the email page to the password page.
• The authentication process aborts immediately with Unknown Error 0x0.

Request

Could you please advise whether this is:

• a known compatibility issue between current Microsoft Authentication Library (MSAL) and macOS Big Sur 11.7.11,
• or another known issue affecting Office activation on Intel Macs running Big Sur?

If there are any diagnostic tools, log collection procedures, or patches available, I would be happy to provide additional information.

Thank you.

Best regards,

Arturas JasinskasDear Microsoft Support,

I am experiencing a persistent activation issue with Microsoft 365 on my Mac.

System information

• MacBook Pro (Retina, 13-inch, Late 2013)
• macOS Big Sur 11.7.11
• Microsoft 365 Personal (active subscription)
• Microsoft account: ******@gmail.com

Problem

Microsoft Word and Excel cannot be activated.

When I choose Already bought Office? Sign in, the applications either:

• immediately display Unknown Error (0x0) before any sign-in page appears,

or

• allow me to enter my email address, but after clicking Next, immediately return:

Unknown Error The error code is: 0x0

The password page never appears.

The same behavior occurs in both Word and Excel.

Subscription status

• Microsoft 365 Personal subscription is active until February 2027.
• I can successfully sign in to:
  • account.microsoft.com
    • office.com
    • The subscription is correctly associated with my Microsoft account.

Troubleshooting already performed

• Completely removed and reinstalled Microsoft Office.
• Tested both Office 16.77 and 16.75.
• Removed Office containers and cache.
• Deleted Microsoft preferences.
• Deleted Group Containers.
• Deleted and recreated Microsoft Registration Database.
• Verified Microsoft Licensing Helper (licensingV2.helper) is running.
• Verified network connectivity.
• Verified HTTPS access to Microsoft authentication servers:
  • https://login.microsoftonline.com (HTTP 200 OK)
  • Verified Safari authentication works normally.
  • Cleared Keychain entries related to Microsoft.
  • Rebooted multiple times.

None of these steps changed the behavior.

Additional observations

• Office successfully reaches the Microsoft authentication service.
• The problem occurs exactly when the application should transition from the email page to the password page.
• The authentication process aborts immediately with Unknown Error 0x0.

Request

Could you please advise whether this is:

• a known compatibility issue between current Microsoft Authentication Library (MSAL) and macOS Big Sur 11.7.11,
• or another known issue affecting Office activation on Intel Macs running Big Sur?

If there are any diagnostic tools, log collection procedures, or patches available, I would be happy to provide additional information.

Thank you.

Best regards,

Arturas Jasinskas

Answer 1

Is there anyway you can upgrade your macOS to at least 12? If your OS is above version 12 but below 14, your office products can be functional, but Microsoft no longer maintains or updates that version. In this scenario, you can install the older downgraded version.

However, if your macOS is below 12, Office products will now enter reduced functionality mode. In other words, the OS is too old to receive the licensing update the Office now requires. Sorry.

This is an update that occured on July 13th and Microsoft shared it here: https://support.microsoft.com/office/update-microsoft-365-or-office-on-your-macos-or-ios-device-f418ae5d-bb5f-4078-b3d9-9340f5dd084e?apid=ets

If your device cannot update its OS to at least 12, your options will be: Use the web version or an alternative like LibreOffice (you want to double check, they may not work under macOS12 either). And you want to cancel your subscriptions.

Your subscription can still work on Windows devices or macOS 12 and above, but if this is the only device you have and cannot upgrade, then I suggest canceling it.