getting html page when trying to access reviewboard diff using rest api

Question

Here is a code review on reviewboard and I was trying to access the diff via rest api.

curl https://reviews.reviewboard.org/api/3184/diff/7/ -H "Accept: application/json"

but this is always giving me a html page.

I tried this and

curl --insecure https://reviews.reviewboard.org/api/3184/diff/7/ -H "Accept: application/json"

it returned me json result but get message object does not exists. not sure what that means !?

{"err": {"code": 100, "msg": "Object does not exist"}, "stat": "fail"}