Laravel controller not responding back on AJAX request

i am typing text in text area

 <input placeholder="DISCOUNT COUPON" type="text" id="coupon">

Sending that text to controller using ajax;

$.ajax({
    type: "POST",
    url: "applyCoupon",      
    data:{
    coupon: $('#coupon').val(),
    course_id: ,
    _token: ,
    },
    success: function(dataResult){
    alert("success");} // why i am not GETTING this alert?

Controller:

public function applyCoupon(Request $request)
    {
        $result=new \stdClass();
        $coupons = Coupons::select('discount_percentage')->where('coupon_code',$request->get('coupon'))
                            ->where('course_id',$request->get('course_id'))
                            ->get();
        $course = Course::findOrFail($request->get('course_id'));
        $discounted_price=  ($course->price) - (($course->price)*($coupons[0]->discount_percentage)/100);

        $result->val = $discounted_price;
        $result->statusCode = 200;
        return json_encode($result);

    }

Web.php:

Route::post('course/applyCoupon', ['uses' => 'CoursesController@applyCoupon', 'as' => 'courses.applyCoupon']);

everything seems fine, but why success function is not running?

via Chebli Mohamed