I have created a Team under my personal Office365 account (a gmail account). I have added multiple users to this team and it has been working fine until now. Today I could not login using my account (owner of Team), I am getting this error:
You're not on Teams yet, but you can set it up for your organization.
Other users can still access this team without issues. And I can login to the team with my work email account (for which I added a user previously). However, this is now a major issue as I cannot 'manage' the team with the 'owner' account.
The main problem appears to be that I cannot login with my personal Office365 account (gmail account).
I think I have seen this problem reported some other times and It's not clear to me why access to Free Teams is lost. Unfortunately, there is not much we, as community, can make here to help with that case apart of asking you to try to access using an inprivate browser session or even the Mobile App...and of course, report the problem so the Microsoft team that is under the support of Free Teams can check what can be happening. For instance, see this thread about a similar problem: https://techcommunity.microsoft.com/t5/Microsoft-Teams/Support-for-Free-Microsoft-Teams/td-p/220051
I had this problem a few weeks ago. I don't even have Office 365 personal subscription, so can't get any support. They either don't want to support me or forward to regular Office support where they don't even know what Teams is.
I was able to fix this. You need to know your tenant's GUID. You can find it in the registration confirmation email. You can probably also see it in the URL when you login with work account or like myself i was able to find it by logging into free Teams SharePoint site and seeing it in the URL. When you have your GUID, then go to https://teams.microsoft.com/_?tenantId=GUID
I followed your advice. The GUID link approach does not work for me, not sure why, just takes me to the /#guestaccount page. However, I found an old email with a link that allows me to sign in to my account. I have not yet decoded which properties in that long email URL does the trick though ... This means I can only sign in to Teams using this link, and cannot use Teams on mobile devices ...
Overall, this is very odd ... Definitely sounds like a backend bug at Microsoft.
For me signing once with GUID fixed it and now i can login just with teams.microsoft.com. You can try connecting to SharePoint https://orgname.sharepoint.com. Maybe this help breaking through. On another thread about problems with logging to free Teams MS representative replied it was a temporary authentication service problem. Though it doesn't seem so.
I guess you should try contacting Office 365 support and file a ticket. Personally i think of free Teams as only a PR stunt.. it could work or not, it can stop working at some point and you are left with no support or even a place to ask.