Pre-flight request blocked

login: function(email, password, callback) {
                alert("In login function");
                $.ajax({
                    dataType: 'json', 
                    contentType: 'application/json; charset=utf-8',
                    url: INSTANCE_URL + '/api/v2/user/session',
					crossDomain: true, //Added this for CORS (Doesn't work)
                    data: JSON.stringify({
                        "email": email,
                        "password": password
                    }),
                    cache:false,
                    method:'POST',
					headers: {
                        "X-DreamFactory-API-Key": APP_API_KEY
                        //"X-DreamFactory-Session-Token": token
                    },
                    success:function (response) {
                        callback(response);
                    },
                    error:function (response) {
                        callback(response);
                        return false;
                    }
                });

I am trying to log users in using this post accessing the api docs on my DreamFactory instance. When I try it locally it works fine, but when I switch over to an official instance I get blocked by a preflight request and get the following error:

XMLHttpRequest cannot load http://52.87.25.0/api/v2/user/session. Response to preflight request doesn't pass access control check: The 'Access-Control-Allow-Origin' header contains multiple values 'http://23.42.248.110, *', but only one is allowed. Origin 'http://23.42.248.110' is therefore not allowed access.

I am using Node.js and I have tried to set the response header and the npm cors package, but neither of those have seemed to make a difference.