WhatsApp error 131026: Message Undeliverable

Code 131026 means WhatsApp could not deliver the message to this recipient and is not going to tell you precisely why. Meta lists the documented reasons: the number is not registered on WhatsApp, the recipient has not accepted the current Terms of Service and Privacy Policy, or the recipient is on a WhatsApp client older than the minimum versions. In practice the same code also covers a recipient who has blocked your business, which Meta does not disclose for privacy reasons.

It usually arrives not in the API response but later, in a statuses webhook with status failed and an errors array containing 131026, because the send was accepted and delivery was attempted afterwards. That timing is why it is easy to miss if you only watch the synchronous response.

Before concluding the recipient is at fault, check your number formatting. A national leading zero or a stray plus sign will produce 131026 for a perfectly valid customer. Your template, token, and account are not the problem.

Do not confuse 131026 with its neighbours: 131049 means Meta deliberately withheld a marketing message, 131050 means the user opted out of your marketing, and 130403 means your own business blocked the user. 131026 is strictly about reachability. Because the platform usually accepts the send and discovers undeliverability afterwards, most occurrences arrive asynchronously - if your webhook pipeline is broken you will never see them, so verify webhook delivery before trusting a low failure count. BSP note: Twilio surfaces the not-a-WhatsApp-user case under its own error namespace (63003, "Channel could not find To address") instead of the Meta code, while API-passthrough providers such as 360dialog return 131026 as-is.

{
  "statuses": [{
    "id": "wamid.HBgLNDQ3NzAwOTAwMTIzFQIAERgSQzY5RkE5RkQ0QkVBNjM0OTlBAA==",
    "status": "failed",
    "timestamp": "1755580800",
    "recipient_id": "447700900123",
    "errors": [{
      "code": 131026,
      "title": "Message Undeliverable",
      "message": "Message Undeliverable",
      "error_data": { "details": "Message Undeliverable." }
    }]
  }]
}

Normalize phone numbers when they enter your system, not at send time, and reject anything that does not parse as a valid E.164 number for its country. Track undeliverable status per contact so campaigns skip them automatically, and watch the 131026 rate per import source; a spike tied to one source almost always means a formatting or data-quality problem upstream. See the WhatsApp error-code guide for the formatting checklist.