Thank you for your reply.
Yes we were affected by the Azure issue yesterday but I believe this user was having the same issue when one of my colleagues previously tried to resolve this issue.
We are getting error 500121 when the second part of the authentication attempts to text or call the user's mobile phone.
I am able to text and call this cell phone. She assures me that SMS is set up on this phone.
I have asked her to restart her phone before she tries it again today.
I have also asked her to try an in-private or incognito browser session in addition to just trying it again because of yesterday's problems.
Do you have any other suggestions to resolve this issue?
thank you in advance for your help