I am trying to pass selected value with ajax to php controller but its not working. This is my code

function prodType() {
    
    $("#productType").change(function(){
        let value = $("#productType").val();
        $.ajax({
            url: "<? echo URLROOT. '/AddProduct'?>",
            type:"GET", //not sure if this should be get or post
            data:{
                "optionValue": value
            },
            success: function(response){
                
            }
        });
    });

I'm sure its getting the value but it is not successfully passing it to the controller.

This is my controller

public function index(){
        $_POST = filter_input_array(INPUT_POST, FILTER_SANITIZE_STRING);
        if($_SERVER["REQUEST_METHOD"]=="POST"){
        ...
    }
    /*If request method == Get, load view */
    else{
        $type = $_POST['optionValue']; //trying to get the value here
        $typeClass = ucfirst($type);
        new Display(new $type);
        var_dump($type); //getting null here
        $this->view('add');
     }
  }

This is my view

 <select id="productType" name="type" onChange="prodType();" required>
      <option value="" hidden>Select type</option>
      <option value="DVDType" >DVD</option>
      <option value="BookType" >Book</option>
      <option value="FurnitureType">Furniture</option>
    </select>

Edited

I changed type from GET to POST and it still didn't work. I am thinking maybe my controller should be this instead

public function index(){
        $_POST = filter_input_array(INPUT_POST, FILTER_SANITIZE_STRING);
        if($_SERVER["REQUEST_METHOD"]=="POST"){
        ...

$type = $_POST['optionValue']; //trying to get the value here
        $typeClass = ucfirst($type);
        new Display(new $type);
        var_dump($type); //getting null here
    }
    /*If request method == Get, load view */
    else{
        
        $this->view('add');
     }
  }

(Getting the value from ajax when the Server request method is POST). Since the value can only be set after the page has been loaded. But then i need the value to be before the form is submitted hence $_POST might not catch it. What am i missing?