I didn’t use curl. I added that configuration to Caddyfile and ran caddy reload. I then visited https://mydomain.com with Chrome and it worked. However https://subd.mydomain.com threw ERR_SSL_PROTOCOL_ERROR error.
PS: My sincere apologies if I’m not testing this the right way. I’m trying to achieve what you described in Serving tens of thousands of domains over HTTPS with Caddy .
It’d have helped a lot if complete Caddyfile configuration was available. I’ve spent ~2 days trying to figure this out.