src/Viserio/Component/Mail/Transport/SparkPostTransport.php
protected function getTransmissionId(ResponseInterface $response): ?string
    {
        $object = \json_decode($response->getBody()->getContents());

        foreach (['results', 'id'] as $segment) {
            if (! \is_object($object) || ! isset($object->{$segment})) {
                return null;
            }

            $object = $object->{$segment};
        }

        return $object;
    }
protected function getTransmissionId(ResponseInterface $response): ?string
    {
        $object = \json_decode($response->getBody()->getContents());

        foreach (['results', 'id'] as $segment) {
            if (! \is_object($object) || ! isset($object->{$segment})) {
                return null;
            }

            $object = $object->{$segment};
        }

        return $object;
    }
Get the transmission ID from the response.

@param \Psr\Http\Message\ResponseInterface $response

@return null|string