When you try to use Remote PowerShell (RPS) in Microsoft Office 365 Dedicated/ITAR, you receive a “0x800434D4L” error message.
This issue occurs if the mailbox is set to enforce Azure Multi-Factor Authentication. Currently, secondary security verification is supported only for browser services and applications. Non-browser applications (rich client applications) do not work with accounts that have this feature enabled.
To work around this issue, use separate user accounts for administrative operations versus non-administrative operations. If necessary, full access permissions for the admin mailbox can be granted to the non-admin account to enable logon.