. . .
print $sock "POST https://$host/ HTTP/1.1\r\n";
print $sock "Connection: close", "\r\n";
print $sock "Host: ", $host, "\r\n";
print $sock "Content-length: ", length $req, "\r\n";
print $sock "Content-type: application/json\r\n";  #RFC 4627
print $sock $req, "\r\n\r\n";

print while <$sock>;   # << ???????

close $sock;