Messenger error 100: Invalid parameter

Code 100 is the Graph API's bad-parameter error: something in your request, an ID, a field, a token parameter, a payload structure, is invalid for this endpoint. Meta's Messenger table lists several strings under the bare code: "Invalid FBID," "No matching user found," and for the marketing-messages system, "notification_messages_token is invalid" and "notification_messages_token has expired," with the blanket advice to "check to make sure the ID or token you are using is valid."

Since April 27, 2026, code 100 also has a new, high-traffic meaning: it is what Meta documents that you receive when a Send API request carries one of the retired message tags, CONFIRMED_EVENT_UPDATE, ACCOUNT_UPDATE or POST_PURCHASE_UPDATE. A bot whose out-of-window notifications suddenly began failing with code 100 in spring 2026 is not suffering a data bug; it is running a flow the platform has since retired. The fix is migration, to HUMAN_AGENT where a human is genuinely replying, or to opt-in mechanisms (one-time notifications, marketing messages) for everything else.

Otherwise, code 100 is a family patriarch whose subcodes carry the diagnosis: 2018001 (no matching user), the media quartet 2018008/2018047/2018109/2018294, 33 (object missing or unreadable), and 2018164 (wrong App ID). Bare 100 with none of those usually means a malformed payload: wrong nesting, missing required field, or an enum value the endpoint does not accept.

{
  "error": {
    "message": "(#100) Invalid parameter",
    "type": "OAuthException",
    "code": 100,
    "fbtrace_id": "BLBz/WZt8dN"
  }
}

Build requests from typed constructors rather than hand-assembled JSON, and validate against the schema before sending. Subscribe to the platform changelog: parameter retirements like the 2026 tag removal are announced ahead of enforcement, and the migration window is when fixes are cheap. The tag rules and every payload cap are tabulated in the Messenger limits reference, with the code-100 family mapped in the troubleshooting guide.