Hi @Robin Chen ,
We can work together to narrow down and resolve the situation. This could be caused by several factors, such as network connectivity, Office application settings, or authentication methods. Here are some possible solutions that you can try:
- Check your network connection and make sure it is stable and reliable. If possible, use a wired connection instead of a wireless one.
- Delete the cached files in Microsoft Office Upload Center.Reference: https://answers.microsoft.com/en-us/msoffice/forum/all/how-to-fix-upload-failed-you-are-required-to-sign/c02b9e8a-1021-4da1-8c8d-0ba4a9486cb9
- Update your Office application to the latest version via File > Account > Update Options > Update Now.
Hope the information can help you. And if there have any unclear or misunderstanding, please feel free to post back and we’ll continue to help you all the time!
Your understanding and patience will be highly appreciated! Hope you have a good day and keep safe!
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