Slack error no_permission: Token lacks permission in this context

The token cleared authentication, but it is not permitted to do this particular thing in this particular place. Slack's own description on chat.postMessage points at the most common concrete case: "Make sure your app is a member of the conversation it's attempting to post a message to." Where missing_scope is about what the token was granted at install, no_permission is about what the token's identity is allowed to do in context — and context usually means channel membership.

The overlap with not_in_channel confuses people: both can appear when a bot posts into a channel it has not joined, with the exact string depending on token type and method. The remediation is the same. For public channels, either invite the bot (/invite @botname) or grant the chat:write.public scope, which lets a bot post to public channels without joining (posting only — reading history still requires membership). For private channels there is no scope shortcut: a member must invite the bot, full stop.

If membership checks out, look at the token's nature. Legacy workspace tokens and certain admin-flavored tokens carry permission models of their own, and calling a method outside that model lands here rather than at missing_scope. When an admin-level method returns no_permission, verify the calling user actually holds the admin role the method requires.

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

Make channel membership part of provisioning: when your app is configured to post somewhere, join public channels programmatically via conversations.join (bot tokens with channels:join) and instruct humans to invite the bot to private ones. Grant chat:write.public if broadcast-to-public-channels is a core behavior, and document which channels the bot genuinely inhabits. See also Slack API limits for per-channel posting ceilings once membership works.