Remove square brackets [] from POST method

I want to admit that I am pretty new to elixir but after digging a little bit I managed to get it to work using this:

Plug Repository

  # covers non-keyword lists
  defp encode_pair(parent_field, list, encoder) when is_list(list) do
    mapper = fn
      value when is_map(value) and map_size(value) != 1 ->
        raise ArgumentError,
              "cannot encode maps inside lists when the map has 0 or more than 1 element, " <>
                "got: #{inspect(value)}"

      value ->
        [?&, encode_pair(parent_field <> "", value, encoder)]
    end

    list
    |> Enum.flat_map(mapper)
    |> prune()
  end

instead of [?&, encode_pair(parent_field <> "[]", value, encoder)] in last line, i just removed the [] like this: [?&, encode_pair(parent_field <> "", value, encoder)]

what I want to know if this is the right way to do it? and would this cause any issues noting that I am only going to be using it for this API call?

you are absolutley right! I am using

  plug(Tesla.Middleware.EncodeFormUrlencoded,
  encode: &Plug.Conn.Query.encode/1,
  decode: &Plug.Conn.Query.decode/1)

thank you for this information

It looks like you may have configured Tesla to use Plug.Conn.Query to encode the params, and it looks like it throws away repeat params, which is how I would have expected to get your thing to work.

I think what I would look at would be passing your own :encode option to Tesla.Middleware.FormUrlencoded that allows duplicates.