Guest to member and log in error

Hi, 

I registered for an Microsoft account in order to use/try Microsoft Teams. 

The problem is this that I was invited as a guest, but it isn't possible to change my account to a member status. In addition I tried to delete my account, but I wasn't able to make a new registry. So I activated my account again to be in a starting situation. But now I'm not able to log in anymore. This message is coming up now:

“AADSTS50020: User account 'XXX@XXX' from identity provider 'live.com' does not exist in tenant 'XXX' and cannot access the application '1fec8e78-bce4-4aaf-ab1b-5451cc387264'(Microsoft Teams) in that tenant. The account needs to be added as an external user in the tenant first. Sign out and sign in again with a different Azure Active Directory user account.“

I don't really know what I have to do exactly. 

I hope you can help me with my request.

Regards,

Soo