Hi @Xu, Dongchen , to resolve this issue, you will need to be added as an external user in the tenant first. You can contact the administrator of the application or your organization's IT department to request that they add your user account as an external user in the tenant. Once your account has been added, you should be able to access the application without any issues.
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