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The request passed every preflight rule we know about, but the upstream platform still said no. This is rare — when it happens we treat it as a gap in preflight coverage and either add a rule or sharpen an existing one.

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What triggers it

  • A platform rule we don’t yet enforce locally — e.g., a content moderation rejection, an account-state issue (rate-limited at the platform level, suspended), or a constraint introduced after our last update.
  • An async media-validation failure on Meta’s container flow (the file passed our size + mime checks but failed deeper inspection).
  • A platform-specific rejection we haven’t translated into a preflight rule yet.

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Response shape

platform_rejected.json
{
  "error": {
    "code": "platform_rejected",
    "message": "Threads rejected the create-container call: media URL not reachable.",
    "rule": "threads.container.error",
    "platform": "threads",
    "platformVersion": "graph-2026-04",
    "platformResponse": {
      "error": {
        "message": "Container creation failed",
        "code": 100,
        "fbtrace_id": "..."
      }
    },
    "remediation": "Verify the media URL returns 200 anonymously, or upload via POST /v1/media first.",
    "docUrl": "https://docs.letmepost.dev/errors/platform_rejected",
    "ruleUrl": "https://docs.letmepost.dev/preflight/threads-container-error",
    "requestId": "req_..."
  }
}
platformResponse carries the raw upstream body, untouched. That’s the most useful signal when this code surfaces — we don’t summarize it away.

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How to handle

  1. Inspect platformResponse for the upstream code / subcode.
  2. If it’s a known opaque rejection (e.g., Instagram’s OAuthException 2207052), check the matching preflight rule page and follow the remediation there.
  3. File an issue: every platform_rejected we see in production is a candidate for a new preflight rule. The dashboard’s post log makes these easy to spot.

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HTTP status

  • 4xx (the platform’s status, passed through) when the upstream said the call is invalid.
  • 502 Bad Gateway when the upstream returned a 5xx — we map upstream 5xx to our 502 + platform_unavailable instead of platform_rejected. See platform_unavailable for that case.