For the Dashboard Analytics API, I think the null response is a result of the endpoint being wrong. I removed the /endpoint prefix and it worked. So the relative endpoint should look like this instead
/api/activity/keys/{keyHash}/{startDay}/{startMonth}/{startYear}/{EndDay}/{EndMonth}/{EndYear}
As for why the ingress is returning 404, I am not sure. The Not Found response looks like the default response of the ingress at the root path or the response when the API listen path does not exist. Could you test with another backend/upstream just to be sure. A test backend I use is https://httpbin.org/anything. It helps with seeing the result of any header, body, parameter or paths that maybe somehow embedded or stripped.
If you still cannot find the root cause then kindly let me know here.