Magento 2 secret key problem

Question

I've a form that performs an Ajax call to a controller, but the response always is You entered an invalid Secret Key. Please refresh the page.

PereiraTech/Faturamento/Controller/Adminhtml/Ac/Index.php

<?php

namespace PereiraTech\Faturamento\Controller\Adminhtml\Ac;

class Index extends \Magento\Backend\App\Action
{
    /**
     * @var \Magento\Framework\Controller\Result\JsonFactory
     */
    protected $resultJsonFactory;

public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\Controller\Result\JsonFactory $resultJsonFactory 
        )
    {
        parent::__construct($context);
        $this->resultFactory = $resultJsonFactory;
    }

    public function execute()
    {
        return $this->resultJsonFactory->create()->setData(['a' => 'b']);
        //return 'test string';
    }

    public function indexAction(){

        //echo 'test string';
    }
}

PereiraTech/Faturamento/view/adminhtml/web/js/form/element/options.js

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

    return select.extend({


    action: function(){            
            var ajaxRequest;
            var param = 'ajax=1';
            ajaxRequest = jQuery.ajax({                
                url: "http://localhost/magento/admin_ptech/faturamento_fat/ac/index",
                type: 'GET',
                data: {param, form_key: window.FORM_KEY},
                dataType: 'json'
            });
                //Show successfully for submit message
            ajaxRequest.done(function (response, textStatus, jqXHR) {
                console.log(textStatus);
                console.log(response);
            });

                //On failure of request this function will be called
            ajaxRequest.fail(function (xhr, status, error) {
                console.log(status);
                console.log(error);
                console.log(xhr.responseText);
                //show error
                console.log('rou');
            });
            return this._super();
        },
    });
});

routes.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:App/etc/routes.xsd">
    <router id="admin">
        <route id="faturamento_fat" frontName="faturamento_fat">
            <module name="PereiraTech_Faturamento"/>
        </route>
    </router>
</config>

If I call just /faturamento_fat/ac/index/ I receive the dashboard html, so I've put the full url to post method.

Edit: If I change from GET to POST, the returned value is a 500 Internal server error problem

Answer 1

The problem was in the type of the request, changing for POST action I was receiving 500 Internal error server, debugging this, I found that the problem was in the PHP file:

This line

$this->resultFactory = $resultJsonFactory;

Should be

$this->resultJsonFactory = $resultJsonFactory;

Answer 2

I have created a sample admin ajax sample extension for you.

Link >> https://github.com/magento1993/adiminajax

Also, you can upload your extension in git so I can check and solve.