foreach issue when using php MVC/ajax/json to delete multiple records

I am listing a table which shows records from the database and each row has a checkbox with an ID value associated with it.

<label class="m-checkbox">
 <input type="checkbox" name="order_id[]" value="<?php echo sanitize($failed->order_id); ?>">
 <span></span>
</label>

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Once the user has selected the checkboxes of the records they want to delete, the submit button is pressed and that triggers an ajax request.

$( '.delete-failed' ).on('click', function(e) {
    e.preventDefault();
    var form = $( '#delete-failed' ).serialize();
    $.ajax({
        url: url + '/TransactionsAjax/deleteFailedTransactions',
        type: 'POST',
        data: form,
        dataType: 'json',
        beforeSend: function() {
            $( 'delete-failed' ).prop('disabled', true);
        }
    })
    .done(function (data) {
        if(!data.success) {
            $( '.alert-danger' ).append(data.message).fadeIn();

        } else {


            $( '.alert-success' ).append(data.message).fadeIn();
        }
    })
            .fail(function (jqXHR, textStatus, errorThrown) {
            console.log(textStatus + ': ' + errorThrown);
            console.warn(jqXHR.responseText);
        });
});

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That then goes to the controller:

if($_SERVER['REQUEST_METHOD'] === 'POST') {

    $response = array();
    $message = '';


    $orderId = $_POST['order_id'];

    $data = [

        'order_id' => $orderId
    ];

    if($this->TransactionsModel->deleteFailedTransactions($data)) {
        $response['success'] = true;
        $response['message'] = 'Failed transactions deleted';

    } else {

        $response['success'] = false;
        $response['message'] = 'Something went wrong. Please try again later.';
    }

    echo json_encode($response);    
}

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Which is supposed to send the data to the model:

public function deleteFailedTransactions($data)
    {
        $this->db->beginTransaction();

        try {

            $this->db->query("DELETE FROM `order_summary` WHERE `order_id` = :order_id");
            $this->db->bind(":order_id", $order_id);

            foreach($data as $item) {
                $order_id = $item['order_id'];
                $this->db->execute();
            }


            $this->db->query("DELETE FROM `order_detail` WHERE `order_id` = :order_id");
            $this->db->bind(":order_id", $order_id);

            foreach($data as $item) {
                $order_id = $item['order_id'];
                $this->db->execute();
            }

            $this->db->commit();
            return true;
        }

        catch(Exception $e) {
            $this->db->rollBack();
            echo $e;
            return false;
        }
    }

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The error I am getting in console is:

undefined index: order_id

It is referring to this line in the model:

$order_id = $item['order_id'];

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I am not sure at which point the problem is, is it in the data being sent via ajax, should the foreach loop be in the controller instead, or.....?