Send string data with jQuery AJAX

I am working on a web project for the university, so I am dealing with AJAX for the first time.
Basically, I would like to create a platform for restaurant employees to manage orders, tables, reservations, and so on.

This is the window to add dishes to an order:

So far I have only interacted with my API by submitting forms. What I would like to achieve here, is that when I click on the + or – symbols, the related dish must be inserted in the database.

Below I will just put a few pieces of code that have to do with my problem.

update.js:

    $(document).on("click", ".add-menuItem-button", function () {
        var id_comanda = $(this).attr("data-id_comanda");
        var id_menu = $(this).attr("data-id_menu");

        $.ajax({
            url: "http://localhost/projects/programmazione_web/api/dettagli_comanda/create.php",
            type: "POST",
            data: id_comanda, id_menu,
            success: function (result) {
                // added to order, notify
                bootbox.alert("Aggiunto alla comanda");
            },
            error: function (xhr, resp, text) {
                // show error to console
                console.log(xhr, resp, text);
                bootbox.alert("Errore");
            }
        });

The following are the PHP functions.

create.php:

// prepare object
$dettagli_comanda = new dettagliComanda($db);

// get id of record to be edited
$data = json_decode(file_get_contents("php://input"));

// make sure data is not empty
if (
    !empty($data->id_comanda) &&
    !empty($data->id_menu)
) {
    // set property values
    $dettagli_comanda->id_comanda = $data->id_comanda;
    $dettagli_comanda->id_menu = $data->id_menu;

    // create new record
    if ($dettagli_comanda->create()) {
        // set response code - 201 created
        http_response_code(201);

        // tell the user
        echo json_encode(array("message" => "Operazione eseguita con successo."));
    }
    // if unable to add new record
    else {
        // set response code - 503 service unavailable
        http_response_code(503);

        // tell the user
        echo json_encode(array("message" => "Non è stato possibile eseguire l'operazione, riprova più tardi."));
    }
}

// if data is empty
else {
    // set response code - 400 bad request
    http_response_code(400);

    // tell the user
    echo json_encode(array("message" => "C'è stato un problema durante l'elaborazione della richiesta, controlla i dati e riprova."));
}

create function in the object.php file:

// create new record
    function create()
    {
        // sql query
        $query = "INSERT INTO dettagli_comanda 
                    SET id_comanda = :id_comanda,
                        id_menu = :id_menu,
                        stato = '0'";

        // prepare query
        $stmt = $this->conn->prepare($query);

        // sanitize
        $this->id_comanda = htmlspecialchars(strip_tags($this->id_comanda));
        $this->id_menu = htmlspecialchars(strip_tags($this->id_menu));

        // bind values
        $stmt->bindParam(":id_comanda", $this->id_comanda);
        $stmt->bindParam(":id_menu", $this->id_menu);

        // execute query
        if ($stmt->execute()) {
            return true;
        }
        return false;
    }

I have tested PHP functions using Postman, and they work without errors.
I’m sure the problem is in the AJAX call, more specifically in passing values.
Anyone know how to help me?

Also, if I can somehow improve the consistency of my question, please let me know.