The problem:   sending ajax requests from HTML5 application on local machine to my API that hosted under IIS on Google Cloud. The facts:  The code looks like:         $.post({             url: apiEndpoint + "Init",             contentType: "application/json; charset=utf-8",             data: data,             success: function (response) {                 logResponse("API response [Init]", response.d);             },             error: function (xhr, status, error) {                 logResponse('Fail to call init API', data);             }         }); The error was looks like: Originally, there was "crossDomain: true" parameter in ...