Discord error 50008: Cannot send messages in a non-text channel

The channel ID you posted to is a type that does not accept messages directly: a category (type 4), a forum (15) or media (16) channel (you post into threads inside them, not into the channel itself), a stage channel in some configurations, or a directory channel. Voice channels have supported text chat for a while, so they are no longer the main cause, but older code that treated every "channel" as postable still trips here.

The usual bug is iterating over guild.channels and sending to each, or letting users pick a destination channel without filtering by type. For forum channels specifically, you must create a thread with an initial message (POST /channels/{id}/threads with a message object) rather than sending to the forum's own ID.

{
  "message": "Cannot send messages in a non-text channel",
  "code": 50008
}

Centralize "where can the bot post" logic in one helper that filters by channel type and by the bot's effective permissions, and use it both for command option validation and for background sends. Store the channel type next to stored channel IDs.

Channel types keep growing, so a capability table beats scattered if-statements. The forum-post creation shape (thread plus starter message) has its own webhook variant with its own error, 220003; channel-type fields and thread rules are on the Discord limits page.