Slack error message_limit_exceeded: Workspace message usage limit reached

This one is about the workspace's plan, not your app's behavior. The chat.postMessage reference documents it as "Members on this team are sending too many messages," pointing at Slack's help article on usage limits for free workspaces. Free-plan workspaces have platform-level usage ceilings, and when the workspace as a whole exceeds them, sends fail with this string regardless of how politely your app paces itself.

Diagnostically that makes it unlike every other rate-limit-family error: there is no Retry-After discipline or queue redesign that fixes it, because the budget being exhausted belongs to the whole team on its current plan. Your app may even be a major contributor — bots' messages count toward what the workspace generates — which is worth knowing before a customer asks why their workspace hit limits.

The realistic paths: the workspace upgrades its plan, overall message volume drops, or the limit period rolls over. Your app's job is to classify the failure correctly (customer-plan issue, not integration bug), reduce its own contribution where possible, and message the workspace owner rather than silently retrying.

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

For products with many free-workspace customers, budget message volume per workspace and prefer fewer, richer messages. Surface a clear in-product notice when this error appears so customers learn the cause from you instead of from silence.