PHP AJAX response.status return undefined

I have two problems really here, the first one being that when I try to evaluate response.status I get undefined and the second one being that my "$_SESSION['promo-code'] = $arr" is also not being created. When entering a promo code, I get the following :

AJAX

	function applyPromo(){
		var promo = $("#promo-code-value").val().trim();
		console.log(promo);
		$.ajax({
			url:"get-promo.php",
			type: "POST",
			data:{ getpromo : promo},
			success: function(response){
				console.log("%j", response);
				console.log(response.status);
				if(response.status === "success"){
					swal("Good job!!", 
						"Promo code applied Successfully!",
						"success"
						).then(() => {
							reloadPage();
						});
					}else{
					swal("Humm...", "Promo code no longervalid","error");
					}	
				}
			})
		}

PHP

if(isset($arr)){
        //Add array to session variable 
        //** Only one code can be apply at the time . will override
        $_SESSION['promo-code'] = $arr; 
        //Success response 
        echo json_encode(array(
            'status' => 'success',
            'message'=> $arr, //For debugging only , will be replaced to success message 
        ));
    }else {
        echo json_encode(array(
            'status' => 'error',
            'message'=> 'error message'
        ));
    }

It's only for a school project. Thanks!!

Ive tried switching "success" to "error" but it is simply not evaluating .I'm new to ajax or php but I believe to have seen others makes it work that way.

The problem one is that response is in JSON. So you have to convert it into JS object and then you can get status. Here is the updated Code:-

function applyPromo(){
   var promo = $("#promo-code-value").val().trim();
   console.log(promo);
    $.ajax({
      url:"get-promo.php",
      type: "POST",
      data:{ getpromo : promo},
      success: function(response){
         let response = JSON.parse(response);
         console.log("%j", response);
         console.log(response.status);
         if(response.status === "success"){
            swal("Good job!!", 
              "Promo code applied Successfully!",
              "success"
            ).then(() => {
               reloadPage();
            });
         }else{
            swal("Humm...", "Promo code no longervalid","error");
         }   
      }
    })
  }

The second problem is that, you are not using session_start(). Here is the updated code:-

if(isset($arr)){
  //Add array to session variable 
  //** Only one code can be apply at the time . will override
  session_start();
  $_SESSION['promo-code'] = $arr; 
  //Success response 
  echo json_encode(array(
     'status' => 'success',
     'message'=> $arr, //For debugging only , will be replaced to success message 
  ));
}else {
  echo json_encode(array(
    'status' => 'error',
    'message'=> 'error message'
  ));
}