How to Fix Microsoft 365 Authentication Couldn’t Be Completed on Windows 11

If you are trying to sign in to Microsoft 365 or any other Microsoft app and are getting the “Authentication couldn’t be completed” error, there's quite a stack of potential things that could be causing the problem. This error also happens on both Windows and macOS operating systems, which means it could be caused by an account, subscription, network, authentication, or Office installation issue. So follow along as we take you through a few different steps you can use to fix the problem.

How to Fix Microsoft 365 Authentication Couldn’t Be Completed on Windows 11

As we mentioned above, this issue might be an authentication issue occurring on Microsoft's end, which means there is nothing you can do to fix it from your end, so first, check whether Microsoft 365 services are working properly. If Microsoft's authentication servers are experiencing an outage, there may be nothing to fix on your device.

Go to the Microsoft service status page and check if the affected services are working. If there is an ongoing incident, wait until Microsoft resolves it and try signing in again.

Also make sure that you are signed into the Microsoft Store with the same account as Office. For whatever reason, a mismatch between the two can cause issues sometimes.

Check Your Microsoft 365 Subscription

If your subscription has expired and you aren't aware of it, that's the primary reason you are getting this error message and can't sign in. So check that you have paid.

• Sign in to your Microsoft account and open the subscription section.
• Check whether Microsoft 365 is listed as an active subscription and verify its renewal date.
• You can also check your order history to confirm that your latest payment or renewal was processed successfully.

Remove Microsoft 365 from any Old Devices

Microsoft 365 subscriptions have device limits. If you have reached the limit, removing an unused device may resolve the authentication problem.

• Sign in to your Microsoft account.
• Open the Devices section.
• Find any device/s you no longer use, and select the option to remove it.

Delete Old Credentials From Credential Manager

Windows may still be using an outdated Microsoft 365 password stored in Credential Manager. This isn't all that common, but it can happen from time to time, so you'll need to purge the old data.

• Search for Credential Manager and open it.
• Select Windows Credentials, find entries related to Microsoft 365, Office 365, or Microsoft Office, and remove the outdated credentials.
• Then restart the Office application and try signing in again.

Contact Your Work or School Administrator

If you are using a work or school account, your organisation may have restricted sign-in or authentication for your account, or they may have forgotten to renew the subscription. So contact your Microsoft 365 administrator and ask them to check your account status, sign-in policies, and authentication settings.

Uninstall Other Office Versions

Having Microsoft 365 installed alongside Office 2024, Office 2021, or another Office version could be causing problems, so get rid of anything that you aren't actively using.

• On Windows, go to Settings > Apps > Installed apps.
• Find the other Office installation, select the three-dot menu, and choose Uninstall.
• Keep Microsoft 365 installed and restart your computer before trying again.

Repair Microsoft 365

If nothing so far has worked you might as well go ahead and repair your Microsoft 365 installation.

• On Windows, go to Settings > Apps > Installed apps.
• Find Microsoft 365, select the three-dot menu, and choose Modify.
• Start with Quick Repair.
• If the problem persists, use Online Repair, which performs a more thorough repair of the installation.

If a Repair didn't fix things, uninstall everything, restart your computer and reinstall it all again.