Dialyzer messages can be pretty obtuse. Usually I take it as a cue to just re-read the function and it's often somewhat clear where the problem lies due to immutability (not always though).

Another trick I'll do, is to use (abuse) pattern matching:

    def foo(%SomeStruct{} = arg, value) when is_integer(value) ...

That also helps Dialyzer narrow down possibilities too and will blow up on runtime.

If you use VSCode, the ElixirLS module will auto-suggest @spec's for your functions.