Callback

<?PHP

function sign($base, $private_key) {
return hash_hmac(“sha256”, $base, $private_key);
}

$request_body = file_get_contents(“php://input”);
$checksum    = sign($request_body, “your secret key here”);

$html = “Request body:  {$request_body}  <br />\n<br />\n”;
$html .= “Checksum: {$checksum}”;

mail(‘your@mail.here’, ‘callbackurl’, $html);