# App The LiSA Player sends a set of essential messages to facilitate communication with the host app or environment, including: * [Heartbeat](/developers/guides/player-communication/message-api-reference/app/app-heartbeat.md) — Signals the player's continued availability. * [Message Acknowledge](/developers/guides/player-communication/message-api-reference/app/app-message-acknowledge.md) — Confirms receipt of a message. * [Message Error](/developers/guides/player-communication/message-api-reference/app/app-message-error.md) — Indicates an issue with a received message. * [Listen](/developers/guides/player-communication/message-api-reference/app/app-listen.md) — Notifies the host that the player is ready for communication. The host app or environment must wait for the [Listen](/developers/guides/player-communication/message-api-reference/app/app-listen.md) message before sending any messages to the LiSA Player. Otherwise, the player may not receive them. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.hello-lisa.com/developers/guides/player-communication/message-api-reference/app.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.