what does unknown error 0x0 mean?

Unknown error 0x0 on Office for Mac is an activation/licensing error. It commonly appears as Unknown Error 0x0 or License not found when launching or activating an Office app on macOS.

For Microsoft 365 or Office installed from microsoft.com, the supported fix is:

1. Make sure the Mac is running macOS 12 or later.
2. Close all Office apps.
3. Open Finder > Applications > Microsoft AutoUpdate.
4. Install all available updates with Update All.
5. Open the Office app again and test activation.

If the apps were installed from the App Store, update them from App Store > Updates instead.

If the error continues after updating:

1. Sign out and sign back in with the Microsoft account that owns the Microsoft 365 subscription.
2. Verify the subscription is present on the Microsoft account services page.
3. Reset Office credentials in Keychain Access by searching for Office and deleting the data license file.
4. If needed, remove old Office license files and reactivate, especially if multiple licenses were used on the Mac.

If the Mac uses a work or school account, the license may not be assigned yet and organizational tech support may need to check it.

References:

• Unknown Error 0x0 or License not found error in Microsoft 365 or Office running on macOS | Microsoft Support
• What to try if you can't install or activate Office for Mac | Microsoft Support
• Activation
• Fixes or workarounds for recent Office installation or activation issues | Microsoft Support