The guest invitation process works as follows:
- A team owner adds a guest to a team.
- The guest receives a welcome email from the team owner, with information about the team and what to expect now that they've been added.
- The guest accepts the invitation. Guests who have a work or school account in Microsoft Entra ID can accept the invitation and authenticate directly. Other users are sent a one-time pass code to validate their identity (One-time passcode authentication required).
- After accepting the invitation, the guest can participate in teams.
If users are asked to enter a password to log in, this may be due to Microsoft Teams' login protection mechanism.
Guests need to have a Microsoft 365 work or school account to authenticate. If the guest does not have a Microsoft account associated with their email address, they will be directed to create a free account.
For issues where the guest user to be added already exists in Microsoft Entra ID, when you try to add a guest user to your Teams.
You may need to contact the team owner or administrator and ask them to check the team's members list to see if this user is already on the list.
If the problem persists, try deleting the user and inviting him again as a guest user after some time.
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