I don’t know if you got a solution with this problem, but I got the same issue and came to a solution.
The “0” means that the browser didn’t get an answer from the server. In this kind of application, the cause could be the whitelist plugin and its bad configuration. First of all you have to check this, in my case it wasn’t.
The issue is from the fact that the SSL is not good enough. To be more specific, if you go to the URL through a browser. On desktop you will never get the issue and the same come with iOS. But with android policy, you will get a message like “Your connection is not private”. That’s why we get a status 0 through the $http requests.
With that thing in my mind, I googled and I found this post : ssl-certificate-is-not-trusted-on-mobile-only
So, I checked the SSL using this website : https://www.ssllabs.com/ssltest/
I found that the intermediate certificate was in SHA1 and it’s deprecated.
I Hope this can help you.
EDIT : After changing the intermediate certificate with another one (SHA2 instead of SHA1), I don’t have this issue anymore.