Delete the 's'
from the URL when you try to access your app, that’s all it takes.
Just make sure you start the Go web server in normal (HTTP) mode. The HTTPS layer is added by the Heroku platform, but your app is still available via both HTTP and HTTPS protocol.
So for example if you access your app using the URL:
https://myapp.herokuapp.com
You may also use
http://myapp.herokuapp.com
solved How to serve Golang app on Heroku using http instead of https?