> ## Documentation Index
> Fetch the complete documentation index at: https://www.plain.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# sendDiscussionMessage

> Send a message in an existing discussion. Supersedes sendThreadDiscussionMessage and additionally
supports Sidekick AGENT_SESSION discussions. For Slack and email discussions, use attachmentIds for
customer-scoped file attachments. For AGENT_SESSION discussions, use workspaceFileIds instead.
The message is delivered to the underlying channel (Slack thread reply, email reply, or agent session).