Moodle for mobile

Hello, I am trying to call a web service that i created on the my Moodle Web version from my Mobile version but I am getting the following error : $mmSite: WS function 'bat_grades_overview' is not available, even in compatibility mode.

From the root directory, my plugin is located in moodle(root)/report/grade/batoverview here is my code. In essence, the mobile version calls the webservice of the web version. Thanks in advance for any help

On the web version (moodle(root)/report/grade/batoverview/db/services.php)

$services = array(
    'bat_overview_service' => array(                                                //the name of the web service
        'functions' => array ('bat_grades_overview', 'bat_grades_details'), //web service functions of this service
        'requiredcapability' => '',                //if set, the web service user need this capability to access
        //any function of this service. For example: 'some/capability:specified'
        'restrictedusers' =>0,    //if enabled, the Moodle administrator must link some user to this service
        //into the administration
        'enabled'=>1,             //if enabled, the service can be reachable on a default installation
    )
);

$functions = array(
    'bat_grades_overview' => array(
        'classname' => 'gradereport_batoverview_external',
        'methodname' => 'get_grades',
        'classpath' => 'grade/report/batoverview/externallib.php',
        'description' => 'Get the user/s report grades table for a course',
        'type' => 'read',
        'capabilities' => 'gradereport/user:view'
    ),
    'bat_grades_details' => array(
        'classname' => 'gradereport_batoverview_external',
        'methodname' => 'get_grades_details',
        'classpath' => 'grade/report/batoverview/externallib.php',
        'description' => 'Get the users detailed report',
        'type' => 'read',
        'capabilities' => 'gradereport/user:view'
    )
);

class gradereport_batoverview_external extends external_api {

    public static function get_grades_parameters() {
        return new external_function_parameters (
            array(
                'courseid' => new external_value(PARAM_INT, 'Course Id', VALUE_REQUIRED),
                'userid'   => new external_value(PARAM_INT, 'Return grades only for this user (optional)', VALUE_DEFAULT, 0)
            )
        );
    }

    public static function get_grades($courseid, $userid = 0) { logic that should be found  by mobile web service call!! }

On the mobile version : 

var data = {courseid: courseId, userid: userId };
return $mmSite.read('bat_grades_overview', data, {}).then(function(rtndata) {
    if(rtndata.length != 0) return rtndata;
    else $q.reject();
});