Hi u201917025,
Thank you for sharing your concern.
Based on the error, OneNote is likely trying to open a notebook that has been moved, deleted, or is no longer accessible with your current work or school account.
Please try the following:
Sign in to OneDrive app using the same work account > Go to My Files > Notebooks folder and check whether the notebook is still listed.
If the notebook is missing, verify whether it was moved, deleted, or if your access has been removed.
If the notebook exists, reset OneNote on your iPad:
Go to Settings > OneNote
Enable Delete All Notebooks and Delete Login Credentials.
Note: Please rest assured that this process only removes locally stored notebook data from your device. It won't delete any notebooks stored in OneDrive or SharePoint. However, any unsynced changes that exist only on the device may be lost. With this in mind, please consider proceeding with this step.
Reopen OneNote and sign in again.
Alternatively, if possible, you can also try opening OneNote on the web and check whether you can access the notebook there.
Please let me know the outcome after trying these steps, and I'll be happy to assist you further.
If you have any questions or need further support, please don’t hesitate to reach out at any time.
Thank you for your patience and understanding.