A technical problem with the server created an error. Try again to continue what you were doing. If the problem persists, try again later. Ajax call

I have a problem here. I use Ajax call to send data to controller.

define([
    'jquery',
    'Magento_Ui/js/form/components/button'
], function($, button){
    'use strict';

    return button.extend({
        defaults: {
            elementTmpl: 'ui/form/element/button',
            imports: {
                data: '${ $.provider }:data'
            }
        },
        initialize: function () {
            this._super();
            console.log('init');
        },
        sendData: function () {
            console.log('ok');
            let id = this.data.id,
                pattern = $('[name="pattern"]').val(),
                addQty = $('[name="add_qty"]').val(),
                addValue = $('[name="add_value"]').val(),
                expiry = $('[name="expiry"]').val(),
                sendData = {
                    'id': id,
                    'pattern': pattern,
                    'add_qty': addQty,
                    'add_value': addValue,
                    'expiry': expiry,
                },
                generateUrl = this.data.generate_url;

            console.log(sendData);
            console.log(generateUrl);
            console.log(id);
            $.ajax({
                type: 'POST',
                url: generateUrl,
                data: sendData,
                dataType: 'json',
                encode: true,
            });
        }
    })
});

Then my controller do its job.

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

namespace BssGiftCardControllerAdminhtmlGiftCode;

use BssGiftCardApiGiftCodeRepositoryInterface;
use BssGiftCardModelGiftCodeFactory;
use MagentoBackendAppAction;
use MagentoBackendAppActionContext;
use MagentoFrameworkAppActionHttpPostActionInterface;
use MagentoFrameworkAppRequestInterface;

/**
 * Class Save saves form
 */
class Generate extends Action implements HttpPostActionInterface
{
    /**
     * @var RequestInterface
     */
    protected $request;

    /**
     * @var GiftCodeFactory
     */
    protected $giftCodeFactory;

    /**
     * @var GiftCodeRepositoryInterface
     */
    protected $giftCodeRepositoryInterface;

    /**
     * @param Context $context
     * @param RequestInterface $request
     * @param GiftCodeFactory $giftCodeFactory
     * @param GiftCodeRepositoryInterface $giftCodeRepositoryInterface
     */
    public function __construct(
        Context                             $context,
        RequestInterface                    $request,
        GiftCodeFactory              $giftCodeFactory,
        GiftCodeRepositoryInterface  $giftCodeRepositoryInterface,
    ) {
        parent::__construct($context);
        $this->request = $request;
        $this->giftCodeFactory = $giftCodeFactory;
        $this->giftCodeRepositoryInterface = $giftCodeRepositoryInterface;
    }

    private function generateCode($pattern) {
        do {
            $code = $pattern;
            while (($pos = strpos($code, "{D}"))) {
                $code = substr_replace($code, chr(rand(48, 57)), $pos, 3);
            }
            while (($pos = strpos($code, "{L}"))) {
                $code = substr_replace($code, chr(rand(65, 90)), $pos, 3);
            }
        }
        while ($this->giftCodeRepositoryInterface->checkExisted($code));
        return $code;
    }

    /**
     * Generate code
     *
     * @return MagentoFrameworkAppResponseInterface|MagentoFrameworkControllerResultJson|MagentoFrameworkControllerResultInterface
     * @throws Exception
     */
    public function execute()
    {
        $resultRedirect = $this->resultRedirectFactory->create();
        try {
            $data = $this->request->getParams();
            if (!isset($data['id'])) {
                $this->messageManager->addErrorMessage("Save Gift Code Pattern first!");
                $resultRedirect->setPath('bss/giftcodepattern/form');
            } else {
                $quantity = (int)$data['add_qty'];
                for ($i = 0; $i < $quantity; $i++) {
                    $resultData = [
                        'pattern_id' => $data['id'],
                        'code' => $this->generateCode($data['pattern']),
                        'status' => MagentoConfigModelConfigSourceEnabledisable::ENABLE_VALUE,
                        'current' => $data['add_value'],
                        'initial' => $data['add_value'],
                        'order' => null,
                        'expiry' => $data['expiry'],
                        'sender_name' => null,
                        'sender_email' => null,
                        'recipient_name' => null,
                        'recipient_email' => null,
                        'message' => null,
                    ];
                    $model = $this->giftCodeFactory->create();
                    $model->addData($resultData);
                    $this->giftCodeRepositoryInterface->save($model);
                }
                $this->messageManager->addSuccessMessage(__(
                    'Save Successfully!'
                ));
                $resultRedirect->setPath('bss/giftcodepattern/form', ['id' => $data['id']]);
            }
            return $resultRedirect;
        } catch (Exception $e) {
            $this->messageManager->addErrorMessage(__(
                'There was an error, please try again!'
            ));
            $resultRedirect->setPath('bss/giftcodepattern/index');
        }
        $resultRedirect->setPath('bss/giftcodepattern/index');
        return $resultRedirect;
    }
}

Then redirect. But I got a problem. My controller generate code and save to database as I expected but NOT redirect.
“A technical problem with the server created an error. Try again to continue what you were doing. If the problem persists, try again later.”


I could’nt find a solution. I think its caused by ajax call. Could u help me to fix this?