Hi Devo,
Thanks for posting in the community. We are happy to help you.
According to the error message, before providing suggestions, I would like to collect more information.
Does the sync problem occur in a specific section or all sections? Does it occur in a specific notebook or all notebooks in the OneNote application?
Some users mentioned that the sync problem only occurred in a specific section. So, they use the Copy or Move function to copy/move all pages from the non-syncing section into another section.
- Therefore, if the problem only occurs in specific sections, you can create a new section, and then use the Copy or Move function to copy one "problematic" page to the new section, and then check again. If the new page is synced well, you can copy all pages.
- If the problem occurs in all sections of the notebook, I suggest you try the following steps to reopen it.
- Please open the notebook in OneNote for Web
You can go to www.onenote.com, sign into your account via the Sign In button in the upper right corner, then try to open the notebook in the browser.
- Please compare the online notebook and the same notebook opened in the OneNote application. If some content hasn't been synced, please manually copy/paste the content to the online notebook. Ensure that the online notebook has the latest content.
- Please close this notebook in the OneNote application. After that, please sign out your account from the OneNote application. Restart the OneNote application and sign into your business account again.
- In OneNote for Web, please click the Editing button> Open in Desktop App to reopen the notebook in the desktop app. After that, please check if the problem still occurs.

If the problem still occurs, please post it back. We will keep on assisting you.
We look forward to your response. Thanks for your cooperation.
Sincerely,
George | Microsoft Community Moderator