Hi @siqiang Yuan , sometimes this means the email has already been used to create an account. Try testing with a new email and let me know if that works. If not, please try the following options for support:
Refer to this FAQ: How do I submit a support request if I can't sign in to the Azure portal?
You can also contact customer service for your country or region.
Please let me know if you have any questions and I can help you further.
If this answer helps you please mark "Accept Answer" so other users can reference it.
Thank you,
James