C++ grpc client to Nginx ssl - c++

Question

I have a grpc server wrapped with nginx.
And I'm trying to write clients to it in different languages.
The python version works well
cred = grpc.ssl_channel_credentials()
channel = grpc.secure_channel(NAME, cred)
stub = MyServiceStub(channel)
But analogical c++ code doesn't.
auto channel = grpc::CreateChannel(NAME, grpc::SslCredentials(grpc::SslCredentialsOptions()));
auto stub = MyService::NewStub(channel);
nginx version 1.16.1 (built with OpenSSL 1.0.2k-fips 26 Jan 2017)
server {
listen 80;
server_name NAME;
location / {
return 302 grpc://NAME$request_uri;
}
}
server {
listen 443 ssl http2;
server_name NAME;
ssl_certificate chain.pem;
ssl_certificate_key privkey.pem;
location / {
grpc_pass grpc://IP;
grpc_read_timeout 3600;
}
}
nginx access log print "PRI * HTTP/2.0" 400 157 "-" "-" "-" and in debug for bad request
[debug] 24255#0: *103047 http check ssl handshake
[debug] 24255#0: *103047 http recv(): 1
[debug] 24255#0: *103047 plain http
[debug] 24255#0: *103047 http wait request handler
but a good request get
[debug] 30192#0: *105029 http check ssl handshake
[debug] 30192#0: *105029 http recv(): 1
[debug] 30192#0: *105029 https ssl handshake: 0x16
[debug] 30192#0: *105029 tcp_nodelay
[debug] 30192#0: *105029 ssl get session: 5F263490:3
grpc version 1.34.0 and c++ client outputs errors
Failed parsing HTTP/2
Expected SETTINGS frame as the first frame, got frame type 80
failed to connect to all addresses
Trying to connect an http1.x server
I find a similar Go problem How to find out why Nginx return 400 while use it as http/2 load balancer? , but don't know how to pass "h2" in c++.