ReCaptcha V2 always returning false even when clicked

Question

I have a form which I'm trying to use Recaptcha on.

I finally wound up just going with this one, which looked almost exactly as my form and PHP files did originally (so that seemed easy enough). Unfortunately, whether Recaptcha checkbox is clicked or not, the "Please check the recaptcha box" error pops up, indicating that it isn't working.

Here is the HTML:

     <form class="contact__form" method="post" action="mail.php">
                                
                                <!-- form message -->
                                <div class="row">
                                    <div class="col-12">
                                        <div class="contact__msg" style="display: none">
                                            <p>Your message was sent successfully.</p>
                                        </div>
                                    </div>
                                </div>
                                <!-- end message -->

                                <!-- form element -->
                                <div class="row">
                                    <div class="col-md-6 form-group">
                                        <input name="name" type="text" class="form-control" placeholder="Name" required>
                                    </div>
                                    <div class="col-md-6 form-group">
                                        <input name="email" type="email" class="form-control" placeholder="Email" required>
                                    </div>
                                    <div class="col-md-6 form-group">
                                        <input name="phone" type="text" class="form-control" placeholder="Phone" required>
                                    </div>
                                    <div class="col-12 form-group">
                                        <textarea name="message" class="form-control" rows="3" placeholder="Message" required></textarea>
                                    </div>
                                    <div class="col-12 form-group">
                                        <div class="g-recaptcha" data-sitekey="6LfrrScdAAAAAM9UdXgQL4bHsISIEtYKW3Yca2Xm"></div>
                                    </div>
                                    <div class="col-12">
                                        <input name="submit" type="submit" class="btn btn-success" value="Send Message">
                                    </div>
                                </div>
                                <!-- end form element -->
                            </form>

PHP:

<?php

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

        // access
        $secretKey = '....';
        $captcha = $_POST['g-recaptcha-response'];

        if(!$captcha){
          echo 'Please check the captcha form';
          exit;
        }

        # FIX: Replace this email with recipient email
        $mail_to = "[email protected]";
        
        # Sender Data
        $subject = "...";
        $name = str_replace(array("\r","\n"),array(" "," ") , strip_tags(trim($_POST["name"])));
        $email = filter_var(trim($_POST["email"]), FILTER_SANITIZE_EMAIL);
        $phone = trim($_POST["phone"]);
        $message = trim($_POST["message"]);
        
        if ( empty($name) OR !filter_var($email, FILTER_VALIDATE_EMAIL) OR empty($phone) OR empty($subject) OR empty($message)) {
            # Set a 400 (bad request) response code and exit.
            http_response_code(400);
            echo 'Please complete the form and try again';
            exit;
        }

        $ip = $_SERVER['REMOTE_ADDR'];
        $response=file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=".$secretKey."&response=".$captcha."&remoteip=".$ip);
        $responseKeys = json_decode($response,true);

        if(intval($responseKeys["success"]) !== 1) {
          echo 'Please check the the captcha form.';
        } else {
            # Mail Content
            $content = "Name: $name\n";
            $content .= "Email: $email\n\n";
            $content .= "Phone: $phone\n";
            $content .= "Message:\n$message\n";

            # email headers.
            $headers = "From: $name <$email>";

            # Send the email.
            $success = mail($mail_to, $subject, $content, $headers);
            if ($success) {
                # Set a 200 (okay) response code.
                http_response_code(200);
                echo 'Thank You! Your message has been sent';
            } else {
                # Set a 500 (internal server error) response code.
                http_response_code(500);
                echo 'Oops! Something went wrong, we couldnt send your message';
            }
        }

    } else {
        # Not a POST request, set a 403 (forbidden) response code.
        http_response_code(403);
        echo 'There was a problem with your submission, please try again.';
    }

?>

And finally, the JS file which is being called in the HTML file with the form:

(function ($) {
    'use strict';

    var form = $('.contact__form'),
        message = $('.contact__msg'),
        form_data;

    // Success function
    function done_func(response) {
        message.fadeIn()
        message.html(response);
        setTimeout(function () {
            message.fadeOut();
        }, 5000);
        
        form.find('input:not([type="submit"]), textarea').val('');
    }

    // fail function
    function fail_func(data) {
        message.fadeIn()
        message.html(data.responseText);
        setTimeout(function () {
            message.fadeOut(5000);
        }, 5000);
    }
    
    form.submit(function (e) {
        e.preventDefault();
        form_data = $(this).serialize();
        $.ajax({
            type: 'POST',
            url: form.attr('action'),
            data: form_data
        })
        .done(done_func)
        .fail(fail_func);
    });
})(jQuery);

Answer 1

that API want POST data, not GET data. for example with hhb_curl i use i've like

        $captcha_response = (new hhb_curl ( 'https://www.google.com/recaptcha/api/siteverify', true ))->setopt_array ( array (
                CURLOPT_POSTFIELDS => array (
                        'secret' => '...',
                        'response' => $_POST ['g-recaptcha-response'],
                        'remoteip' => $ip 
                ) 
        ) )->exec ()->getResponseBody ();
        $captcha_response = json_decode ( $captcha_response, true , 999, JSON_THROW_ON_ERROR);
        if($captcha_response ['success'] !== true) {
            http_response_code ( 400 );
            header ( "content-type: text/plain;charset=utf8" );
            die ( 'reCaptcha error!: ' . hhb_return_var_dump ( $captcha_response  ) );
        }