How to fix "AADSTS900561: The endpoint only accepts POST requests. Received a GET request."

Question

I am currently stuck trying to log in to my company’s SharePoint folder.

After logging in, the system asks me to confirm my identity by sending a text message to my phone. However, when I try to proceed, I receive the following error:

Error Code: 399287

[Moderator's note: PII removed]

Timestamp: 2026-03-12T22:12:54Z

The message indicates that there is a problem confirming my identity (shown below in Portuguese):

"Confirmar a sua identidade

Lamentamos, mas estamos com problemas a verificar a sua conta. Tente novamente."

I believe that if I could use another authentication method instead of the text message to my phone, I might be able to complete the verification step.

At the moment, I urgently need access to my data stored in SharePoint, and this situation is very frustrating.

Does anyone have suggestions on how to resolve this issue?

Thanks,

Maria

Answer 1

Dear @Maria Barros,

Thank you for posting your question in the Microsoft Q&A forum.

I apologize for any inconvenience you may encounter when using our services/ products. Based on your description:

As a moderator, I do not have the tools to investigate your specific account directly because this is a user-to-user support forum. Moderators and contributors, including external Microsoft employees, cannot directly intervene in Microsoft product features or access back-end systems. Our role is limited to providing technical guidance on reported issues, requests, or ideas. However, I will try my best to guide you as clearly as possible.

Because this sign-in issue is related to account security and data protection, changes to multi-factor authentication (MFA) methods must be performed by the Global Administrator of the organization's tenant to protect your account and organizational data. How do I find my Microsoft 365 admin? - Microsoft Support

As the next step, please contact your IT Admin (the Global Administrator of the tenant) and ask them to require you to re-register multi-factor authentication for your account. Once they trigger MFA re-registration, you be prompted to set up your authentication method again at next sign-in, and you can choose a more reliable option (such as Microsoft Authenticator) if available in your organization. Please send them this article if they do not know what to do: Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID | Microsoft Learn

I sincerely apologize for the frustration this has caused and thank you for your understanding.