Forum Discussion
ATP connectivity challenge HTTP Error 400
My issue was resolved by offboarding from a different tenant and onboard subsequently.
Even if you reset the device, if it has been part of a previous poc on atp the onboarding will fail.
and if we can't remember the tenant that we used before to login and get the offboarding script I assume there is nothing else we can do?
Support was looking at creating an offboarding script based on data found in the registry. There wasn't an easy way to create that ourselves. I managed to find my tenant back and eventhough it had long expired I could still log into it and download an offboarding script. If you still know what mailbox the poc was requested in you might find the mail with your login. It should contain this string Analyst@Windows.
Good luck
For anyone else having a similar problem you can use the MDATPClientAnalyzer tool at
https://docs.microsoft.com/en-us/windows/security/threat-protection/microsoft-defender-atp/configure-proxy-internet#verify-client-connectivity-to-microsoft-defender-atp-service-urls
It finds the issue I was having and that I need to off-board my device from my previous Azure Tenant.