Are you running https://play.dgraph.io/? If so, It won’t work due Google’s restrictions to CORS. No external application can access any internal (LAN or Localhost) services such as Router admin page, UPnp in general and any localhost service. Also HTTPS services are blocked to access non-HTTPS.
The solution, give a cert to your Dgraph cluster or run Ratel locally. Or use some Browser that hasn’t adopted this rule.