Better reason

exception3.php

<?php

if ($response->getStatusCode() >= 400) {
    $code = $this->extractErrorCode($response->getBody());

    switch ($code) {
        case FailReasons::NO_TAGS:
            $msg = 'The document has not enough signature tags';
            break;
        //...
        default: $msg = $this->getBodyContentAsString($response->getBody());
    }

    throw new BadSigningRequest($msg);
}