Live chat API error codes

Branch on error.code.

Code	Status	What to do
`conversation_closed`	422	Website chats accept messages only while open; reopen a conversation before changing its mode.
`conversation_not_found`	404	No conversation with that id that this key can see.
`text_required`	400	The message has no content for its channel (text, html, a template or attachments).
`integration_paused`	409	An agent paused integration replies on this conversation. Stop retrying; a `conversation.updated` event tells you when it resumes.
`website_not_allowed`	403	The key is limited to other websites.
`agent_not_found`	422	`assigned_agent_id` is not an active agent in this workspace.
`idempotency_key_reused`	422	The Idempotency-Key was already used with a different request.
`idempotency_in_progress`	409	A request with this Idempotency-Key is still being processed. Retry shortly.