There are two types of guest authentication: passcode and password authentication.
By unifying to one that demands improvement.

https://docs.microsoft.com/en-us/microsoftteams/guest-access

"The guest accepts the invitation. Guests who have a work or school account in Azure Active Directory 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). "

There are two ways that end users can get confused.
As an example, by forgetting the registered password, which hinders smooth access.

From a usability point of view, this behavior needs to be improved.