External Sharing - Registered with Microsoft Account

Hi all,

We had a user share a OneDrive folder with an external user. The external user clicked the link and was prompted for a Microsoft login after entering their email address. My guess is that at some stage, they associated their work email with a Microsoft account and forgot about it?

Anyway, I'm just wondering is it possible to allow external users use a One Time Passcode for situations like this? Or would they have to reset their MS account?

I could be wrong with what happened here, just my best guess.