grpc-web example don't work

Hi, I tried using the example in the tutorial of grpc-web(link: https://grpc.io/docs/platforms/web/basics/), but I am receiving the following error:
POST http://localhost:8080/EchoService/Echo net::ERR_CONTENT_LENGTH_MISMATCH 503 (Service Unavailable)
I am using webpack as in the tutorial, using envoy as proxy in localhost(where my grpc server is running and where I access the website from) my website host is AWS ubuntu machine with a simple http server using the http-server command.

Any help would be highly appreciated.