we are seeing a 403 - Forbidden not sure what happened......

Are you able to log-in using the default administrator account?
Are you using a SSL certificate? If so, is the certificate still valid?
If you're using SSO/silent authentication, check if there are any issue with the agent providing Appian with the valid header details
Is this dev or test or prod? If prod, please raise a support ticket with Appian support for assistance
For dev/test, were any recent changes or bulk modifications done to user identity? Did you configure LDAP settings etc., that the system is no longer able to use/reach?

Are you able to log-in using the default administrator account?
Are you using a SSL certificate? If so, is the certificate still valid?
If you're using SSO/silent authentication, check if there are any issue with the agent providing Appian with the valid header details
Is this dev or test or prod? If prod, please raise a support ticket with Appian support for assistance
For dev/test, were any recent changes or bulk modifications done to user identity? Did you configure LDAP settings etc., that the system is no longer able to use/reach?