It’s probably because “server: true” is not configured on the endpoint. By default, in dev environment phoenix server is only started if you start the app with mix task, as in “iex -S mix phx.server” or “mix phx.server”… If you just start the app with “iex -S mix” no server starts unless you tell Phoenix to start it automatically.
This is precisely the same case with releases. If you intend to start your app in dev mode as a release, flip the “server: true” flag in confing, just like it is in prod.exs:
config :my_app, MyApp.Endpoint,
server: true,
...
