Proxy not working if Browser.application is used

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Is this a bug report?

Yes

Environment

1. node -v: v16.10.0
2. npm -v: 7.24.1
3. npm ls create-elm-app -g:
   /usr/local/lib
   └── create-elm-app@5.22.0

Then, specify:

1. Operating system: macOS Catalina 10.15.7 19H1419 x86_64

Steps to Reproduce

1. Start a JSON API server at http://localhost:8081 serving an /items endpoint
2. Add this to elmapp.config.js

   module.exports = {
     proxy: "http://localhost:8081",
   }

3. Create Elm app like:

   main : Program () Model Msg
   main =
       Browser.application
           { view = view
           , init = \_ -> \_ -> \_ -> init
           , update = update
           , subscriptions = always Sub.none
           , onUrlRequest = \_ -> NoOp
           , onUrlChange = \_ -> NoOp
           }

4. Start elm app with npx elm-app start

Expected Behavior

http://localhost:3000/items should serve the JSON

Actual Behavior

Serves the same Elm app as under http://localhost:3000

---

I assume that the problem is the interaction with Browser.application, but I'm not sure about that.

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So the proxy is actually working, but you can't open it in the browser! 😅
Because of the requested Content-Type I guess?

I leave this issue open as "Improve documentation on how proxy is working exactly"