Slack error restricted_action: A workspace preference blocks this posting

The workspace's own settings — not your token, not your scopes — forbid this action. Slack's description: "A workspace preference prevents the authenticated user from posting." Admins can restrict who may post in specific channels (announcement-style channels are the canonical case), and when your app or user falls outside that allowlist, the API refuses with restricted_action.

This family has documented, more specific siblings on chat.postMessage for particular channel configurations: restricted_action_read_only_channel ("Cannot post any message into a read-only channel"), restricted_action_thread_only_channel ("Cannot post top-level messages into a thread-only channel"), and restricted_action_thread_locked ("Cannot post replies to a thread that has been locked by admins"). Whichever variant you receive, the meaning is the same: posting rights in this channel are managed by workspace policy, and code cannot override policy.

Treat it as a routing problem. Either the bot needs to be granted posting rights in that channel by an admin, or the message belongs in a channel the bot may actually post to. Retrying is pointless; the answer will not change until a human changes the channel's settings.

{"ok": false, "error": "restricted_action"}

During onboarding, validate each configured destination channel with a low-stakes test post and surface policy failures to the installing admin immediately, rather than discovering them when a critical alert fails to deliver. Keep an explicit allowlist of destination channels under the app's control and re-validate when admins change channel settings.