In certain cases, you might need to disable Two-Factor Authentication for the users logging into the MDM MSP console. You can do so as explained below:
You can refer to these troubleshooting steps and retry logging in.
In this case, an Admin or technician with sufficient previlege can resend the QR code by navigating to Admin -> User Administration(under Global Settings) and clicking on the ellipsis icon under Action, present against the user to whom the QR code is to be sent. Select Resend QR code from the dropdown and the QR code is mailed to the user, after which they can retry logging in.
If there are no administrators available or you are the only administrator, you can disable TFA as explained below:
NOTE: You can Two-Factor Authentication on MDM MSP server again as explained here.