Better exception names

exception2.php

<?php
//....
$action = DocumentSigningAction::create($doc);

/** @var \Psr\Http\Message\ResponseInterface $response */
$response = $action->execute();

if ($response->getStatusCode() >= 500) {
    throw new SigningServiceUnavailable();
}

if ($response->getStatusCode() >= 400) {
    throw new BadSigningRequest();
}