How to use SNI of SSL by ocaml-ssl?

I want to check a expiration date of SSL(Certificate) and i use ocaml-ssl for that.

There is a server and this server accepts some domains.

e.g.: and
these domain have same IP address.
and each domain have different Certificate of course.

I try to get the information of each Certificate with ocaml-ssl.
I think, i have to use Ssl.Ssl.set_client_SNI_hostname function for that because server accepts two domains.

therefore wrote like following code:

  let ctx = Ssl.create_context Ssl.TLSv1_2 Ssl.Client_context in
  Ssl.set_context_alpn_protos ctx ["h2"; "http/1.1"];
  let sockaddr = Unix.ADDR_INET (Unix.inet_addr_of_string ("SOME_IP_ADDRESS"), 443) in
  let socket_domain = Unix.domain_of_sockaddr _sockaddr in
  let socket = Unix.socket socket_domain Unix.SOCK_STREAM 0 in

  let ssl = Ssl.embed_socket socket ctx in
  Ssl.set_client_SNI_hostname ssl "";

  let _ = try
      Ssl.connect ssl;
    with _ ->
      Printf.printf "%s\n" (Ssl.get_error_string());

But following error occurred by Ssl.connect ssl.


How can I switch domains with ocaml-ssl?
I can use Ssl.open_connection_with_context ctx sockaddr in simply then it works fine.
But domain is not changable.