HTTPS with $http in Angular not working

I'm building a Facebook Tab using Angular. I'm doing a $http request to a PHP page on the same domain. The request looks like this:

$http({
    method: 'JSONP',
    url: '/api?action=saveResult&points=' + state.points + '&callback=JSON_CALLBACK',
    cache: false
});

The app is served with HTTPS but when I try to run the app in a Facebook tab I get the following mixed content error:

Mixed Content: The page at 'https://example.com' was loaded over HTTPS, but requested an insecure script 'http://ift.tt/1IDxQ2M'. This request has been blocked; the content must be served over HTTPS.

I have also tried putting the full URL with HTTPS in the $http method, but I still get the same error.