Messenger error 100: Failed to fetch the file from the URL

Code 100 with subcode 2018008 means Meta's fetcher could not download the attachment you referenced by URL. When you send media with payload.url, the platform does not trust your bytes, it fetches them itself from your server, and that fetch is subject to the conditions the error message enumerates: a valid URL, a valid SSL certificate, an acceptable file size, and a server that responds fast enough to avoid timeouts.

Each clause is a distinct failure class. "Valid URL" fails on localhost addresses, intranet hosts, redirects to login pages, and URLs with unencoded characters. "Valid SSL certificate" fails on self-signed, expired, or incomplete-chain certificates, browsers forgive an incomplete chain because they cache intermediates; Meta's fetcher does not. "Valid file size" ties to the platform's 25 MB attachment cap. And "responding fast enough" catches cold serverless functions, slow image resizers, and CDNs that block unfamiliar user agents; for video specifically, the related 2018294 documents a 75-second ceiling on the fetch.

The classic production trap is asset URLs that work in the office: behind a VPN, allow-listed by IP, or served by a staging host the internet cannot reach. Meta fetches from its own infrastructure, so the test that matters is a plain curl from a cloud host with no special access. The alternative that removes this class of failure entirely is the Attachment Upload API: upload once, get a reusable attachment_id, and stop depending on your edge at send time.

{
  "error": {
    "message": "(#100) Failed to fetch the file from the url",
    "type": "OAuthException",
    "code": 100,
    "error_subcode": 2018008,
    "fbtrace_id": "BLBz/WZt8dN"
  }
}

Serve bot media from a boring place: public CDN, long-lived URLs, correct content types, no auth, no geo rules. Upload frequently used assets once via the Attachment Upload API and reference IDs thereafter, faster for users and immune to your edge's moods. The media size and timeout numbers are tabulated in the Messenger limits reference; delivery debugging is in the troubleshooting guide.