Error Request Failed - Service Unavailable (503) or Request Timed Out when trying to log in to HipChat Server for iOS

Summary

The application is not allowing users to log in due to "Request failed - service unavailable (503) error.  
Users also may not be able to reach the server from iOS when typing in the HipChat Server hostname and clicking "next". The app will time out before reaching the login page.

Environment

HipChat for iOS 3.16.0

Steps to Reproduce

1. Open HipChat for iOS
2. Select HipChat server option
3. Type in the hipchat server hostname
   OR
4. Insert email address and password and try to log in

Expected Results

The application should allow users to log in successfully.

Workaround

Temporarily provide access to HipChat over HTTP (port 80).