Hi @pierre coetzer
There are many reasons why you can't sign in. First of all, you need to isolate whether the issue is a desktop application, log in to the Teams web client in privacy mode to see if the problem persists.
If you're still having issues with Teams web client, you can try contacting your admin to run the following tests to troubleshoot.
- Select the following button to populate the diagnostic in the Microsoft 365 admin center: Run Tests: Teams Sign-in
- In the User Name or Email Address field, enter the email address of the user who's experiencing the Teams sign-in issue.
For more details about Teams sign-in errors, you could refer to:
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