Binance.create_listen_key

You're seeing just the function create_listen_key, go back to Binance module for more information.
Link to this function

create_listen_key()

Creates a socket listen key that later can be used as parameter to listen for user related events.

Returns {:ok, %Binance.DataStream{}} or {:error, reason}.

Example

{:ok,
  %Binance.DataStream{
    listen_key: "pqia91ma19a5s61cv6a81va65sdf19v8a65a1a5s61cv6a81va65sdf19v8a65a1"
  }
}

For more context please read https://github.com/binance/binance-spot-api-docs/blob/master/user-data-stream.md#create-a-listenkey