Binance.close_listen_key

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

close_listen_key(key)

Closes/disables the listen key. To be used when you stop listening to the stream.

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

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