Problems signing in to MS Teams

Hi zuzanna670

This occurs if the domain on your email (i.e. username@domain.com) has been used before - could have been a trial with another microsoft product such as Power BI, Office 365 or something else

2 real ways to solve this

1.) Contact Microsoft support to remove the domain from the other account

https://support.microsoft.com/en-gb/contactus/

2.) Create another microsoft account and sign up

https://account.microsoft.com/account

Hope that answers your question. It is frustrating, and most people end up picking option 2 over option 1. However, if you want to use that domain with Teams here you'll need to get Microsoft to remove it from the account which somebody used previously

Best, Chris