Send an agent chat message and manage an active chat via the LiveChat Agent Chat API

Steps

1. Authenticate as an agent: either use a Personal Access Token (created in Developer Console under Settings > Authorization > Personal Access Tokens) sent as HTTP Basic auth with your account_id as username, or complete an OAuth 2.1 flow (implicit or authorization-code) against https://accounts.livechat.com/ to get a Bearer access_token.
2. Call the Web API action endpoint pattern POST https://api.livechatinc.com/v3.6/agent/action/<action> (or use the RTM/websocket transport for a persistent agent session) with the Bearer or Basic-PAT authorization header and Content-Type: application/json.
3. To send a message, call the send_event action with a JSON body containing the chat_id and an event object (type: "message", the message text, and optional recipients: all or agents) — this is the same action used by the LiveChat Node.js SDK's sendMessage(chatId, message) helper.
4. To read or manage chats first, use the corresponding Agent Chat API actions (e.g. list/get chat actions) before sending events, since send_event requires the requesting agent to already be a participant on the chat.
5. Subscribe to real-time updates (new messages, routing changes) via RTM incoming_event pushes, or register a webhook via the Configuration API if you're using the stateless Web API transport instead of the websocket.