I have tried on two different accounts, one with trial and other enterprise account, but not getting alert emails for http response codes.
I have two flows that return status codes 400 and 500, and they work as intended, responding correct response codes and the dashboard shows response codes but getting no emails for alerts.
Any other alert works just fine, just this response code doesn't work.
Help!
Found the answer.
It was because in the project, API Auto-discovery in Global Properties wasn't referencing to the flows I was testing 400 and 500 response alerts. Adding references fixed the issue.