Angularjs - Cannot pass parameter

I'm using angularjs for my mobile app project. My problem is I can't pass my all my parameters to my own API. My API can't detect any post parameters that my app send to it.

$http.post("http://xxxxxxxx/api/verify_login.php", {
    "username": "admin",
    "password": "12345678",
    "secret_key": "123456789"
}).success(function(data, status, headers, config) {
    alert(JSON.stringify(data));
}).error(function(data, status, headers, config) {
    alert(JSON.stringify(status));
});

If using POSTMAN it works.

Please advice. Thank you.

how about this :

var postData = '{"username":"'+varUsername+'", "password" : "'+varPassword+'", "secret_key" : "'+varSecretyKey+'"}';

$http({
    method: 'POST',
    url: 'http://xxxxxxxx/api/verify_login.php',
    data: postData,
    headers: {'Content-Type': 'application/x-www-form-urlencoded'}
}).success(function(response) {
        $scope.result = response;
        alert(JSON.stringify(data));
    });

This will post data as : 

username=hisname&password=hispassword&secret_key=hiskey

keep in mind that, angularjs will automatically convert your postdata as JSON.

Looks like this StackOverflow answer helps solve half the problem. Look at the accepted answer. To paraphase the quote on this post:

By default, jQuery transmits data using Content-Type: x-www-form-urlencoded and the familiar foo=bar&baz=moe serialization. AngularJS, however, transmits data using Content-Type: application/json and { "foo": "bar", "baz": "moe" } JSON serialization, which unfortunately some Web server languages—notably PHP—do not unserialize natively.

There is a nice way to get it do this - override the default transformRequest - this is show in a nice post by Ben Nadel here - Here's a snippet:

var request = $http({
    method: "post",
    url: "process.cfm",
    transformRequest: transformRequestAsFormPost,
    data: {
        id: 4,
        name: "Kim",
        status: "Best Friend"
    }
});

He has a fairly simple implementation - if you find that this doesn't work for you, you can use the a detailed version here - you can inject this factory in your controller.

.factory("transformRequestAsFormPost", function() {
    function transformRequest(data, getHeaders) {
        var headers = getHeaders();
        headers["Content-type"] =
            "application/x-www-form-urlencoded; charset=utf-8";
        return (serializeData(data));
    }
    return (transformRequest);

    function serializeData(data) {
        if (!angular.isObject(data)) {
            return ((data === null) ? "" : data.toString());
        }
        var buffer = [];
        for (var name in data) {
            if (!data.hasOwnProperty(name)) {
                continue;
            }
            var value = data[name];
            buffer.push(encodeURIComponent(name) + "=" + encodeURIComponent((value ===
                null) ? "" : value));
        }
        var source = buffer.join("&").replace(/%20/g, "+");
        return (source);
    }
});