Hi Rachel,
Thank you for posting, I am here to help you today. May i know if the mail that you are using is personal account or Organization / School account?.
This will help us to give you correct steps for Troubleshooting.
For the meantime try this steps:
If you unable to log in using the Authentication app. try our sign in helper
click this link to open sign in helper:
https://go.microsoft.com/fwlink/?linkid=2214157
The tool will ask you to enter the email address or mobile phone number you're trying to sign in with and check the details you provide. If we detect a problem with your account, we'll tell you what you need to do to solve the problem. If we don't detect any problem, we'll guide you through how you can help yourself.
I hope you find this information helpful. Please let us know if you have any further questions If the answer is helpful, please click "Accept Answer".
Best regards,
Jansher