private function createAcceptRequest($shipmentDigest)
    {
        $xml = new DOMDocument();
        $xml->formatOutput = true;

        $container = $xml->appendChild($xml->createElement('ShipmentAcceptRequest'));
        $request = $container->appendChild($xml->createElement('Request'));

        $node = $xml->importNode($this->createTransactionNode(), true);
        $request->appendChild($node);

        $request->appendChild($xml->createElement('RequestAction', 'ShipAccept'));
        $container->appendChild($xml->createElement('ShipmentDigest', $shipmentDigest));

        return $xml->saveXML();
    }