Http2 fails for http requests

I am working on enabling http2 for our kong app. Enabled http2 on 8000 like this.


When I tested grpc service on 8000 port got a valid response but when i try http service on 8000 got following error

curl -X POST localhost:8000/httptest
Warning: Binary output can mess up your terminal. Use "--output -" to tell 
Warning: curl to output it to your terminal anyway, or consider "--output 
Warning: <FILE>" to save to a file.

Isnt http2 backward compatible and support http and http2 requests. Can someone pls let me know what am i missing