This proof of concept periodically polls data from a specific API before decoding the JSON. It should create a list of atoms from the binary keys it receives the first time it queries the API for reuse with each subsequent poll.

defmodule ProofOfConcept do
  def naive_string_to_atom(raw_json) do
    {:ok, decoded_api_response} = Jason.decode(raw_json)

    root_keys = 
    decoded_api_response
    |> List.first()
    |> Map.keys()

    nested_keys =
      Enum.flat_map(
        root_keys,
        fn key ->
          decoded_api_response
          |> Enum.map(fn map_element ->
            foo = Map.get(map_element, key)

            case is_map(foo) do
              true ->
                Map.keys(foo)

              false ->
                :not_a_key
            end
          end)
          |> Enum.reject(&(&1 == :not_a_key))
        end
      )
      |> Enum.flat_map(& &1)
      |> Enum.uniq()

    
      extracted_keys = 
      (nested_keys ++ root_keys)
      |> Enum.map(&String.to_atom(&1))

      IO.inspect(extracted_keys, limit: :infinity)
  end

  def decode(raw_json) do
    try do
      Jason.decode(raw_json, keys: :atoms!)
    rescue
      _ ->
        IO.puts("Converting JSON keys to atoms . . . ")
        naive_string_to_atom(raw_json)
        main()
    end
  end

  def main() do
    api_url = "https://wavescap.com/api/assets.json"
    {:ok, api_response} = HTTPoison.get(api_url)

    decode(api_response.body)
  end
end

The problem:
Apparently the atomized keys are never retained in memory, requiring them to be recreated each time updated data is retrieved from the API.

iex(1)> ProofOfConcept.main
Converting JSON keys to atoms . . . 
[:firstPrice_brln, :firstPrice_btc, :firstPrice_cnyn, :firstPrice_eth,
 :firstPrice_eurn, :firstPrice_gbpn, :firstPrice_jpyn, :firstPrice_ngnn,
 :firstPrice_rubn, :firstPrice_tryn, :firstPrice_uahn, :"firstPrice_usd-n",
 :firstPrice_waves, :lastPrice_brln, :lastPrice_btc, :lastPrice_cnyn,
 :lastPrice_eth, :lastPrice_eurn, :lastPrice_gbpn, :lastPrice_jpyn,
 :lastPrice_ngnn, :lastPrice_rubn, :lastPrice_tryn, :lastPrice_uahn,
 :"lastPrice_usd-n", :lastPrice_waves, :"24h_vol_brln", :"24h_vol_btc",
 :"24h_vol_cnyn", :"24h_vol_eth", :"24h_vol_eurn", :"24h_vol_gbpn",
 :"24h_vol_jpyn", :"24h_vol_ngnn", :"24h_vol_rubn", :"24h_vol_tryn",
 :"24h_vol_uahn", :"24h_vol_usd-n", :"24h_vol_waves", :circulating, :data,
 :excludedFromCirculating, :id, :name, :precision, :sender, :shortcode, :start,
 :totalSupply, :trades, :website]

Converting JSON keys to atoms . . . 
[:firstPrice_brln, :firstPrice_btc, :firstPrice_cnyn, :firstPrice_eth,
 :firstPrice_eurn, :firstPrice_gbpn, :firstPrice_jpyn, :firstPrice_ngnn,
 :firstPrice_rubn, :firstPrice_tryn, :firstPrice_uahn, :"firstPrice_usd-n",
 :firstPrice_waves, :lastPrice_brln, :lastPrice_btc, :lastPrice_cnyn,
 :lastPrice_eth, :lastPrice_eurn, :lastPrice_gbpn, :lastPrice_jpyn,
 :lastPrice_ngnn, :lastPrice_rubn, :lastPrice_tryn, :lastPrice_uahn,
 :"lastPrice_usd-n", :lastPrice_waves, :"24h_vol_brln", :"24h_vol_btc",
 :"24h_vol_cnyn", :"24h_vol_eth", :"24h_vol_eurn", :"24h_vol_gbpn",
 :"24h_vol_jpyn", :"24h_vol_ngnn", :"24h_vol_rubn", :"24h_vol_tryn",
 :"24h_vol_uahn", :"24h_vol_usd-n", :"24h_vol_waves", :circulating, :data,
 :excludedFromCirculating, :id, :name, :precision, :sender, :shortcode, :start,
 :totalSupply, :trades, :website]

Converting JSON keys to atoms . . . 
[:firstPrice_brln, :firstPrice_btc, :firstPrice_cnyn, :firstPrice_eth,
 :firstPrice_eurn, :firstPrice_gbpn, :firstPrice_jpyn, :firstPrice_ngnn,
 :firstPrice_rubn, :firstPrice_tryn, :firstPrice_uahn, :"firstPrice_usd-n",
 :firstPrice_waves, :lastPrice_brln, :lastPrice_btc, :lastPrice_cnyn,
 :lastPrice_eth, :lastPrice_eurn, :lastPrice_gbpn, :lastPrice_jpyn,
 :lastPrice_ngnn, :lastPrice_rubn, :lastPrice_tryn, :lastPrice_uahn,
 :"lastPrice_usd-n", :lastPrice_waves, :"24h_vol_brln", :"24h_vol_btc",
 :"24h_vol_cnyn", :"24h_vol_eth", :"24h_vol_eurn", :"24h_vol_gbpn",
 :"24h_vol_jpyn", :"24h_vol_ngnn", :"24h_vol_rubn", :"24h_vol_tryn",
 :"24h_vol_uahn", :"24h_vol_usd-n", :"24h_vol_waves", :circulating, :data,
 :excludedFromCirculating, :id, :name, :precision, :sender, :shortcode, :start,
 :totalSupply, :trades, :website]

Converting JSON keys to atoms . . . 
[:firstPrice_brln, :firstPrice_btc, :firstPrice_cnyn, :firstPrice_eth,
 :firstPrice_eurn, :firstPrice_gbpn, :firstPrice_jpyn, :firstPrice_ngnn,
 :firstPrice_rubn, :firstPrice_tryn, :firstPrice_uahn, :"firstPrice_usd-n",
 :firstPrice_waves, :lastPrice_brln, :lastPrice_btc, :lastPrice_cnyn,
 :lastPrice_eth, :lastPrice_eurn, :lastPrice_gbpn, :lastPrice_jpyn,
 :lastPrice_ngnn, :lastPrice_rubn, :lastPrice_tryn, :lastPrice_uahn,
 :"lastPrice_usd-n", :lastPrice_waves, :"24h_vol_brln", :"24h_vol_btc",
 :"24h_vol_cnyn", :"24h_vol_eth", :"24h_vol_eurn", :"24h_vol_gbpn",
 :"24h_vol_jpyn", :"24h_vol_ngnn", :"24h_vol_rubn", :"24h_vol_tryn",
 :"24h_vol_uahn", :"24h_vol_usd-n", :"24h_vol_waves", :circulating, :data,
 :excludedFromCirculating, :id, :name, :precision, :sender, :shortcode, :start,
 :totalSupply, :trades, :website]

Converting JSON keys to atoms . . . 
[:firstPrice_brln, :firstPrice_btc, :firstPrice_cnyn, :firstPrice_eth,
 :firstPrice_eurn, :firstPrice_gbpn, :firstPrice_jpyn, :firstPrice_ngnn,
 :firstPrice_rubn, :firstPrice_tryn, :firstPrice_uahn, :"firstPrice_usd-n",
 :firstPrice_waves, :lastPrice_brln, :lastPrice_btc, :lastPrice_cnyn,
 :lastPrice_eth, :lastPrice_eurn, :lastPrice_gbpn, :lastPrice_jpyn,
 :lastPrice_ngnn, :lastPrice_rubn, :lastPrice_tryn, :lastPrice_uahn,
 :"lastPrice_usd-n", :lastPrice_waves, :"24h_vol_brln", :"24h_vol_btc",
 :"24h_vol_cnyn", :"24h_vol_eth", :"24h_vol_eurn", :"24h_vol_gbpn",
 :"24h_vol_jpyn", :"24h_vol_ngnn", :"24h_vol_rubn", :"24h_vol_tryn",
 :"24h_vol_uahn", :"24h_vol_usd-n", :"24h_vol_waves", :circulating, :data,
 :excludedFromCirculating, :id, :name, :precision, :sender, :shortcode, :start,
 :totalSupply, :trades, :website]

After each new API poll, why aren’t the atoms that were previously generated being reused?