Changing between multiple Teams Free accounts within the app or browser
Hello,
Can you launch a web browser, and tell me if you can sign into your business account here:
https://myaccount.microsoft.com
If you can, then see if you can sign into Teams here: https://teams.microsoft.com/v2?
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As for your personal Microsoft account invitation email issue, you need to have a native outlook.com username in order for the calendar/invitation reply to work. Can you tell me, what happened when you tried to change your account's alias, what error did you run into? Or are you stuck at the step where it asks for verification code that you cannot access?