Discord error 20016: Slowmode rate limit

The channel has slowmode enabled (rate_limit_per_user between 1 and 21,600 seconds) and the acting user has posted more recently than the slowmode interval allows. This is a per-user, per-channel cooldown set by server moderators, not a Discord API rate limit, even though it is delivered as HTTP 429.

Bots are exempt from slowmode when they hold Manage Channel or Manage Messages in that channel, which is why most bots never see this. If your bot is a plain member with only Send Messages, it is subject to slowmode like any user. You also see 20016 when acting on behalf of a user through OAuth2 (user tokens), where the bot's own permissions do not apply.

The retry_after in the body tells you how long the cooldown has left; it can be minutes, not milliseconds.

{
  "message": "The resource is being rate limited.",
  "retry_after": 11.42,
  "global": false,
  "code": 20016
}

Document Manage Messages as a required permission for channels where the bot posts frequently, and include it in your invite URL's permission bits. Respect the channel's slowmode setting when you cannot get that permission: cache rate_limit_per_user from CHANNEL_UPDATE and throttle locally.

Slowmode is a channel setting, so the durable fix is social as much as technical: agree with the server's moderators whether the bot should bypass it. The slowmode range and the exemption rule are on the Discord limits page, and the general 429-handling pattern in http 429 applies to the retry.