The fix has gone out. Access has been returned. The team will continue monitoring the situation closely.
Posted Jun 17, 2020 - 19:23 UTC
The team is currently working on a fix for an issue, which started on the latest update at 17.37GMT, that prevents additional users from accessing organisations. In addition, this same issue is causing problems on checkout for a small percentage of all users.
The fix is expected to go out in the next 10 minutes.