The websocket output is a stream of messages, with the above message ID, or a far end message ID. The websocket is used for asynchronous/random reception of messages. For some API endpoints, the response is via the websocket because there could be a long wait state for the Lightning Network to forward the messages. In our design, these GRPC/REST interfaces, generate a message ID, fire off the message into the Lightning Network, and then immediately respond to the developer with the message ID. The developer then monitors the websocket for that message ID to return. It is recommended to always monitor the websocket for asynchronous incoming messages. Do not transmit INTO the websocket, it will be ignored.