Send html Form or Post data to Sendgrid contact list

How to Send html Form or Post data to Sendgrid contact list using PHP through API using JSON

################################## API ##############################

$curl = curl_init();

$list_ids="<<Your Contact List ID>>";

$first_name=$_POST['first_name'];

$last_name=$_POST['last_name'];

$email=$_POST['email'];

curl_setopt_array($curl, array(

  CURLOPT_URL => "https://api.sendgrid.com/v3/marketing/contacts",

  CURLOPT_RETURNTRANSFER => true,

  CURLOPT_ENCODING => "",

  CURLOPT_MAXREDIRS => 10,

  CURLOPT_TIMEOUT => 30,

  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,

  CURLOPT_CUSTOMREQUEST => "PUT",

  CURLOPT_POSTFIELDS => "{\"list_ids\":[\"$list_ids\"],\"contacts\":[{\"address_line_1\":\"string (optional)\",\"address_line_2\":\"string (optional)\",\"city\":\"string (optional)\",\"country\":\"string (optional)\",\"email\":\"$email\",\"first_name\":\"$first_name\",\"last_name\":\"$last_name\",\"postal_code\":\"string (optional)\",\"state_province_region\":\"string (optional)\",\"custom_fields\":{}}]}",

  CURLOPT_HTTPHEADER => array(

    "authorization: Bearer SG.XXXXXXXXXXXXXX",

    "content-type: application/json"

  ),

));

$response = curl_exec($curl);

$err = curl_error($curl);

curl_close($curl);

if ($err) {

  echo "cURL Error #:" . $err;

} else {

  //echo $response;

    $_SESSION['message'] = "Thank You, we will get back to you in the next few days";

    

    if(isset($_POST['contactus'])){

        header('Location: contact.php');

    } else{

        eader('Location: sign-up.php');

    }

}

################################## API ##############################