Ajax submission leads to => An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (2 MB) that

So i’m trying to submit a form using ajax, in my form i have the following:

        $form['actions']['#type'] = 'actions';
        $form['actions']['submit'] = array(
        '#type' => 'submit',
        '#value' => $this->t('OK'),
        '#button_type' => 'primary',
        '#prefix' => '<div class="tc btn_pay relative">',
        '#suffix' => '</div>
                        </div>',
        '#attributes' => array(
            'class' => array('proximabold', 'tc', 'transition', 'no-underline', 'ph3', 'pv2', 'mb2', 'dib', 'white'),
        ),
        '#ajax' => [
            'event' => 'click',
            'callback' => '::updateTable',
            'wrapper' => 'table-wrapper',
            'progress' => [
                'type' => 'throbber',
                'message' => t('Verifying entry...'),
            ],
        ],
    );

and a simple updateTable function:

public function updateTable(array $form, FormStateInterface $form_state) {
    return "Hello World";
}

But when i click on submit i get the error: An unrecoverable error occurred. The uploaded file likely exceeded the maximum file size (2 MB) that this server supports.

I knew that the error is server side (Maybe i’m wrong), so i went to php.ini (i use PHP7) and update the following lines:

post_max_size = 6144M
memory_limit = 6144M
upload_max_filesize = 6144M
max_file_uploads = 1000

but without luck, this configuration shouldn’t be necessary as the request size is only 1.5KB

Drupal version: 


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