main.php

<?php 
  
  //This is error reporting turn on if your having issues with PHP.
  error_reporting(-1);
  ini_set('display_errors', 'On');
  set_error_handler("var_dump");

  //This helps in showing each post key and value turn on when needed also make sure you have data argument in post function
  
  // foreach ($_POST as $key => $value) {
  //   # code...
  //   echo "<p><strong>" .$key. ":</strong>" .$value. "</p>";
  // }

  //if form is submitted.
  if(isset($_POST['submit'])) {

    //if captcha response is given
    if(isset($_POST['recaptcha']) && $_POST['recaptcha']) {
      //test the captcha response for correctness.
      $secret = '6LfkIBEUAAAAAD1SyJeqyBYu-NhyzPvWr4UpkVtM';
      $captcha_response = $_POST['recaptcha'];
      $verify_url = file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=".$secret."&response=".$captcha_response);
      $json_array = json_decode($verify_url, true);
      
      //if json_array contains a true response to the success key.
      if($json_array['success']) {
        //Email information
        $admin_email = "asifrmemon@gmail.com";
        $email = $_POST['email'];
        $subject = $_POST['subject']." *From Your Website*";
        $message = $_POST['message'];
        $headers = "From: ".$admin_email."\r\n".
        'Reply-To: '.$email;

        //send email
        mail($admin_email, $subject, $message, $headers);
      }
    }
  
  } 

?>