private static function serializePayload($payload = '') : string
    {
        // If the payload is already JSON, return it
        if (\is_string($payload)) {
            return $payload;
        }

        $data = '';

        if (!empty($payload)) {
            $data = \json_encode($payload, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_PRESERVE_ZERO_FRACTION);
        }

        return $data;
    }