I would guess the Elixir would print out the full module path, so this is wrong.MyApp in the error above is referring to the module Mix.Tasks.MyApp, you need to define that first.
To also prevent confusion, I would recommend doing an abbreviation of some sort–this also adds the convenience of making it easier to type in the terminal, e.g. mix phx.gen.new vs mix phoenix.generate.new
edit: I tested this locally and it seems to work fine, so the above seems to be wrong. I just suspected some sort of module shadowing was taking place
