How to handle errors centrally?

In my local instance, it throws the error with proper error codes. On prod deployed to fly, it just throws a 500 status error.

In my tests I have to use assert_error_sent to make tests pass. When i try to assert conn.status it just throws an error in test module.

conn = post(conn, `route`, %{})
assert conn.status == 400

This is what my code looks like… works fine in dev locally but throws 500 error in prod.

defmodule KayaanPrintsWeb.Router do
  use KayaanPrintsWeb, :router
  use Plug.ErrorHandler
  require Logger

 
  @impl true
  def handle_errors(conn, %{kind: kind, reason: reason, stack: stack}) do
    error_string = log_error_string(kind, reason, stack, conn)

    case reason do
      %Phoenix.Router.NoRouteError{} ->
        Logger.error(error_string)

        conn
        |> put_status(:not_found)
        |> json(%{error: "Route not found"})
        |> halt()
  
     ....other error cases handling