Map to what exactly, what shape of data do you want? If you want to decode a json object into an elixir map, you can use a json decoder, there are several.

The most popular is probably GitHub - devinus/poison: An incredibly fast, pure Elixir JSON library · GitHub, with it your code would be like this:

resp = HTTPoison.get!(url)
json = Poison.decode!(resp)

Here, json is an elixir term, probably a map. So you’d be able to use it to populate your table.

You can’t do that directly, because you have list there. I will give you 4 example ways to achieve what you need:

1. Get first item using List.first/1 or last item using List.last/1
2. Get by specified index using Enum.at/2
3. Iterate over list and do something for every item in it using Enum.each/2 or Enum.map/2 (depends on what you need).
4. Find element which is interesting for you by using Enum.find/2

For example:

list = Poison.decode!(response.body)
first_item = List.first(list)
last_item = List.last(list)
n = 10
nth_item = Enum.at(list, n) # where n is integer
found_item = Enum.find(list, & &1["Payor"] == "ASMSI")

# Then you can fetch specified data as you wanted:
%{"InvoiceDetails" => invoicedetails} = first_item
%{"InvoiceDetails" => invoicedetails} = last_item
%{"InvoiceDetails" => invoicedetails} = nth_item
%{"InvoiceDetails" => invoicedetails} = found_item

# Or do something for every item in list

defmodule Example do
  def sample_each(list), do: Enum.each(list, &do_sample_each/1)

  defp do_sample_each(%{"InvoiceDetails" => invoicedetails}), do: IO.inspect(invoicedetails)

  def sample_map(list), do: Enum.map(list, &do_sample_map/1)

  defp do_sample_map(%{"InvoiceDetails" => invoicedetails}), do: invoicedetails
end

:ok = Example.sample_each(list) # debugs "InvoiceDetails" for every item
invoicedetails_list = Example.sample_map(list) # returns list of invoicedetails

I think it’s both. He’s struggling with creating an impossible pattern match in order to support an unworkable template structure.