Hi @Walid Issa
According to your case description, you encountered an error when accessing Notebook in Microsoft Teams, but it works fine when opened in the browser. It is recommended that you try the following solutions:
Clear Teams cache:
Re-sign in: Try to sign out of Teams and then sign in again. This can refresh your session and solve some temporary problems.
Update Teams app: Make sure you are using the latest version of Microsoft Teams. Or try reinstalling Teams.
Use the desktop version of OneNote: If you have the OneNote desktop application, you can try to open Notebook in the desktop application to see if it works properly.
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