My company recently upgraded our cell phones and I ran into some issues recently where my users kept getting the 2 digits or kept asking for passcodes. it was not going to the right device or the user did not have the correct account showing on their device. The account was showing as a Microsoft Entra Id and not our company name. i wanted to try and sync the account again so i went thru several times and disabled and then re-enforced their account along with checking the box to require user to provide contact methods again. Nothing was working so i disabled temporarily to allow the users to sign in to the mdm on the devices. I was researching and stumbled upon some information on a forum that helped me to remove the old devices from the users that had authenticator issues and then had them resync their authenticator and it worked. Maybe there is a different method that is faster but this is what has been working for me as a newer admin that wasnt shown a whole lot with how to fix microsoft issues.
see if your admin can go to the Microsoft Entra Admin Center. On the left side, expand the Protection menu and then click on the authentication methods. Under basic information, i clicked on the # of users link and searched for users that were having issues. i clicked on their name to get into their profile and then looked for the MFA status box and clicked on the manage authentication methods link in the same box. i could see a device assigned under the authentication method that i would then delete using the ellipsis menu on the right of the device line. Once i deleted that, i informed the user to login to office.com to start the syncing with authenticator and it would not trigger those previous issues and could now get to the qr code. then on the device, i would tell them go to authenticator and click to add a new accunt and scan the qr code to sync. once they did that, we clicked next on the screen with the qr code and the user was getting their push notification and the 2 digit number was showing up for them to approve.