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Check that the user is using Safari, Chrome, or Firefox.
Instruct the user to clear their browser cache and/or history, and then log in again.
If this doesn’t solve the problem, submit a ticket at support@terracotta.education.
*It is possible that this error could be caused by a problem with a WAF (web application firewall) on Terracotta’s side or on the institution side. Please let us know if the error persists so we can troubleshoot!