Can't set ssl httpchk

Everything is OK before I add this code in the section backend:
option httpchk
http-check connect port 443 ssl sni
http-check send meth HEAD uri / ver HTTP/1.1 hdr host
http-check expect status 200-399
server public weight 3 check

## is my proxy server, I connect to via it to check the status of proxy
But I can’t connect to the server, the stats page says:
Layer4 connection problem: Connection refused