Messenger error 4: Application request limit reached

Code 4 is the Graph API's application-level throttle: your app, across every Page and every endpoint it touches, has exceeded the platform rate limit for its rolling window. Meta's Messenger error-codes table lists two message variants, "Application request limit reached" and "Too many send requests to phone numbers," and the prescribed remedy is the same for both: "pause requests until current requests drop below the limit."

Because the quota is app-wide, code 4 has a failure mode the per-Page throttles lack: one noisy tenant can take down every Page the app serves. A multi-Page bot platform where a single Page runs a runaway campaign will see error 4 on unrelated Pages, which looks like a mysterious global outage until you sum call volume per app rather than per Page. The Messenger-specific ceilings (200 calls x engaged users per 24 hours, 300 sends per second per Page) are enforced separately and surface as 613 or 80006; code 4 sits above all of them.

The platform tells you how close you are before it cuts you off. Every response carries an X-App-Usage header with call_count, total_time and total_cputime as percentages; throttling begins when any of them reaches 100. Ignoring that header and discovering the limit via error 4 is the avoidable part.

{
  "error": {
    "message": "(#4) Application request limit reached",
    "type": "OAuthException",
    "code": 4,
    "fbtrace_id": "Fz54k3GZrio"
  }
}

Centralize every Graph API call behind one client that enforces a token-bucket budget, watches X-App-Usage, and treats 80% as the alarm line. Cache anything cacheable, user profiles especially, and replace polling with webhooks. The documented Messenger ceilings that sit underneath the app quota are tabulated in the limits reference, and the throttling family is mapped in the troubleshooting guide.