Hi @Valeri Georgiev ,
In my experience, this issue has multiple possible causes, including the following:
Cause 1: SomeOne has already set up Teams for you.
Resolution 1: Look for an invitation in your email Inbox. Alternatively, try to sign in to Teams from a private or incognito
browser window. To do this, right-click this Teams link, select the appropriate option depending on your browser (for example, select Open link in inPrivate window in Edge), and then enter your domain credentials to sign.
Cause 2: Your email address is tied to both a work and a personal account. For example, you're using contoso.com domain for both your Microsoft Service Account (Live ID) and your work account (Active Directory).
Resolution 2: Try to create a Teams account in a new private or incognito browser window. To do this, right-click this Teams link, select the appropriate option depending on your browser (for example, select Open link in inPrivate window in Edge), and then enter the credentials for your work or school account instead of for your personal account to sign in. If that doesn't work, you must unlink the two accounts to create a free Teams account. For more information, see the "I want to use a different email address or phone number to sign in" section in Change the email address or phone number for your Microsoft account.
Cause 3: You're trying to sign up for your work account by using a free tenant.
Resolution 3: Use your organization's tenant for this account. For personal use, create a free Teams account by using a personal email address.
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