Several things:
Not every version of curl supports HTTP/2. Secondly, if yours does you need to specify this in your curl command.
curl --http2 https://domain.com
What does https://tools.keycdn.com/http2-test show when you test your domain with it?
Did you confirm that your
ssl.conf
file for the domain you want to use HTTP/2 showslisten 443 ssl http2;
?