I also posted this question to https://stackoverflow.com/q/57939468/4766.
I have GraphiQL (running in Chrome on macOS) in advanced mode setup with my Elixir/Phoenix/Absinthe web server. It works great for queries and mutations, but when I try a subscription I get: “Subscriptions cannot be run over HTTP. Please configure a websocket connection”:
It works with GraphiQL in simple mode:
And it works with GraphiQL in playground mode:
Is this a bug in advanced mode? Or am I failing to configure it properly?