Messenger error 2: Unexpected error - retry later

Code 2 is the Graph API's service-trouble signal: "An unexpected error has occurred. Please retry your request later." The error-handling guide files it as "API Service: temporary issue due to downtime, wait and retry the operation." Meta's Messenger error-codes table gives the same advice, check the Meta Developer Platform status page when it appears, and then adds a caveat unique to this platform: "You might also receive this error if a customer has blocked your business from messaging him or her."

That caveat changes how a Messenger bot should treat code 2. On most Graph surfaces it is purely transient and retry-safe; on Messenger sends, a persistent code 2 for one specific recipient may actually be a blocked relationship wearing the wrong error, behavior normally announced by 551. The retry policy should therefore be scoped: retry a handful of times with backoff, but if one PSID keeps failing while others succeed, reclassify that contact as possibly-unreachable rather than retrying forever.

The distributional test is the quickest diagnosis. Errors spread across many recipients and endpoints, with Meta Status showing an incident: transient, pause and drain later. Errors concentrated on one recipient while the rest of the queue flows: recipient-side, suppress the contact. Its transient siblings 1 and 1200 share the retry machinery; only code 2 carries the documented blocked-customer ambiguity.

{
  "error": {
    "message": "An unexpected error has occurred. Please retry your request later.",
    "type": "OAuthException",
    "code": 2,
    "fbtrace_id": "Fz54k3GZrio"
  }
}

Same discipline as all transients: durable queue, backoff, idempotency, and status-page awareness in the pager runbook. Add the per-recipient failure counter, it is the only way to catch the documented blocked-customer case hiding inside a transient code. The classification logic for 1, 2 and 1200 versus the permanent family is drawn out in the Messenger troubleshooting guide.