Getting null response to Recaptcha V3 with ajax - php

Question

I'm having a problem with getting a problem when submitting captcha v3 to ajax. I get a null response to Google. I have tried multiple tutorials but I think it does not fix to ajax request.
I think the problem is with google or my php, or ajax request. I understand my codes but I am not familiar with using google's code like this captcha v3. I have use captcha v2 before. And now I am trying v3 I can't run it with my code.
Here is my Ajax and HTML code :
// when form is submit
$('.contact-form').submit(function (event) {
// we stoped it
event.preventDefault();
var url = $(this).prop('action');
var contact_data = $(this).serialize();
$('.btn-contact').html('<em class="fas fa-spinner fa-pulse"></em> Sending...');
$('.alert').fadeOut('slow');
// needs for recaptacha ready
grecaptcha.ready(function () {
// do request for recaptcha token
// response is promise with passed token
grecaptcha.execute('6Ldjp6Q[--my site key---]8H5bxI1', { action: 'create_contact' }).then(function (token) {
// add token to form
$('.contact-form').prepend('<input type="hidden" name="g-recaptcha-response" value="' + token + '">');
var contact = function () {
$.ajax({
type: 'POST',
url: url,
dataType: 'json',
data: contact_data, token: token ,
success: function (response) {
$('.message').html(response.message);
$('.btn-contact').html('<em class="fas fa-paper-plane"></em> Send');
if (response.error) {
$('.status').removeClass('alert-success').addClass('alert-danger').show();
}
else {
$('.status').removeClass('alert-danger').addClass('alert-success').show();
$('.contact-form')[0].reset();
}
}
});
};
setTimeout(contact, 3000);
});;
});
});
<?=form_open('Contact/Send_Contact', array('class' => 'contact-form'))?>
<div class="row top-2">
<div class="col-md-12">
<div class="status alert text-center" style="display:none;">
<button type="button" class="close clearMsg"><span aria-hidden="true">×</span></button>
<span class="message"></span>
</div>
</div>
<div class="form-group col-md-6">
<input type="text" placeholder="Your Name" name="name" class="form-control name">
<div class="invalid-feedback invalid-name"></div>
</div>
<div class="form-group col-md-6">
<input type="email" placeholder="Your Email" name="email" class="form-control email">
<div class="invalid-feedback invalid-email"></div>
</div>
<div class="form-group col-md-12">
<input type="text" placeholder="Subject" name="subject" class="form-control subject">
<div class="invalid-feedback invalid-subject"></div>
</div>
<div class="form-group col-md-12">
<textarea placeholder="Message" class="form-control message_text" name="message" rows="4"></textarea>
<div class="invalid-feedback invalid-message"></div>
</div>
<div class="col-md-12">
<button type="submit" class="btn btn-info btn-contact float-right"><em class="fas fa-paper-plane"></em> Send</button>
</div>
</div>
</from>
<script src="https://www.google.com/recaptcha/api.js?render=6Ldj[--My site key--]5bxI1"></script>
And I also copied some PHP code and I don't know where is the problem here because this is my first time using CodeIgniter and I also haven't used captcha v3 too.
Please review my PHP code here :
public function Send_Contact() {
$output['error'] = true;
$output['message'] = 'Please fill up the error field(s).';
$name = $this->input->post('name');
$email = $this->input->post('email');
$subject = $this->input->post('subject');
$message = $this->input->post('message');
$captcha = $this->input->post('token');
$this->form_validation->set_rules('name', 'Name', 'required');
$this->form_validation->set_rules('email', 'Email', 'required');
$this->form_validation->set_rules('subject', 'Subject', 'required');
$this->form_validation->set_rules('message', 'Message', 'required');
if($this->form_validation->run() === false) {
//some codes here I remove because it has nothing to do with the question.
die(json_encode($output));
}
if(!$captcha){
$output['message'] = "Invalid catpcha";
die(json_encode($output));
}
$secretKey = "6Ldjp[--My secret key--]YQL_";
$ip = $_SERVER['REMOTE_ADDR'];
// post request to server
$url = 'https://www.google.com/recaptcha/api/siteverify';
$data = array('secret' => $secretKey, 'response' => $captcha);
$options = array(
'http' => array(
'header' => "Content-type: application/x-www-form-urlencoded\r\n",
'method' => 'POST',
'content' => http_build_query($data)
)
);
$context = stream_context_create($options);
$response = file_get_contents($url, false, $context);
$responseKeys = json_decode($response,true);
if($responseKeys["success"]) {
if($this->contact_model->create_contact()) {
$output['error'] = false;
$output['message'] = 'Thank you for sending message! <em class="far fa-check-circle"></em>';
echo json_encode($output);
} else {
$output['error'] = true;
$output['message'] = 'Error in database model.';
echo json_encode($output);
}
} else {
$output['message'] = "Invalid catpcha";
die(json_encode($output));
}
}
I'm using codeigniter 3. and this public function is in the contact controller.