Can AutoCert in Golang use custom ports if a proxy is forwarding?

Question

In Golang, with autocert, I keep seeing examples like this:

server := &http.Server{
        Addr:      ":https",
        Handler:   r,
        TLSConfig: &tls.Config{
            GetCertificate: certManager.GetCertificate,
        },
    }

    go http.ListenAndServe(":http", certManager.HTTPHandler(nil))

However, I have a server with many sites (go apps) and I use NGINX to proxy the traffic. Can I do something like this?

server := &http.Server{
        Addr:      ":8443",
        Handler:   r,
        TLSConfig: &tls.Config{
            GetCertificate: certManager.GetCertificate,
        },
    }

    go http.ListenAndServe(":8080", certManager.HTTPHandler(nil))

If not, are there any other solutions for this?

If so, I'm not sure what I could be doing wrong. I do see that one of the returns of the certManager.GetCertificate method is error.

So second part of this question is, how can I catch certManager.GetCertificate's error? My app loads and compiles fine. No errors are thrown.