Tomorrow HTTP stream may slightly change its behavior.
During multiple data delivery to your endpoint within a single connection (Connection: keep-alive should be activated on your server) when stream will encounter Accept-Encoding header as a response from your server with either deflate or gzip value it will enable automatic compression of its contents starting from the next data portion in the same connection.
To enable such behavior and minimize traffic ensure that your server responding with next HTTP headers:
This is optional of course and up to you.
For the very first request within a new connection only uncompressed data (as it is now) will be send. In case of your server will reply any http error code the stream will reset connection and retry data delivery in a new connection, always uncompressed.
Please check your http stream and your endpoint server logs for any details. We will activate this mode in next 24 hours.