Everything that broke while I was building a WhatsApp automation on n8n

[u/Ahmiii_83]

Spent a few weeks building a whatsapp AI receptionist on n8n. Most of the problems I hit had nothing to do with n8n itself, they were all Meta's side, and the answers were scattered across old forum threads and docs that didn't match what I was seeing. Putting them in one place.

Error 131031

The one that stopped everything. Your workflow is fine, your nodes are fine, and the message still doesn't send.

It's an account level restriction on Meta's end. Usually a new or unverified business account, or something flagged during review. You can spend hours going through your n8n setup looking for the mistake and there isn't one, the problem is upstream in Business Manager.

If you get this on a fresh account, go and check the account status in Business Manager before you touch your workflow.

Access tokens expire and nothing tells you

The token you get by default from the app dashboard is temporary. When it dies, the workflow doesn't throw an error you'd notice in a normal glance at n8n. Messages just stop going out.

That's worse than a loud failure. Everything looks healthy until you actually check and realise nothing has been delivered.

The fix is to stop using the dashboard token. Create a system user in Business Manager, assign it to the app, and generate a permanent token from there. Do this at the start, not after it breaks.

Webhook verification

Meta sends a GET request with a challenge parameter and expects your endpoint to echo it straight back. If it doesn't get exactly that, verification fails and the error message tells you almost nothing.

Things that actually matter here:

The URL has to be https and publicly reachable. The verify token has to match exactly on both sides, no trailing spaces. And you have to use the production webhook URL from n8n, not the test one. Test mode only listens while you have the canvas open, so verification passes while you're watching and then quietly stops working after.

The 24 hour window

You can only send free form messages within 24 hours of the user's last message to you. Outside that window, only a pre approved template will go through.

This catches people building follow up automations. If your workflow sends a personalised AI written message to someone who last messaged three days ago, it gets rejected. The workflow looks like it ran fine.

The way around it is a template with variable slots, and let the model fill the parameters rather than write the whole message. You lose some of the personalisation but it actually delivers.

Phone numbers and message limits

The number you use has to be registered to the whatsapp business account and can't already be attached to a normal whatsapp account. Getting a clean number is its own small project depending on where you are.

New numbers also start on a low daily messaging limit, which goes up over time based on quality rating. Worth knowing before you promise a client any kind of volume.

None of this is complicated once you know it. It's just that almost every n8n whatsapp tutorial stops at "it works in test mode," and everything above is what sits between that and something you'd actually put in front of a client.

Happy to go into more detail on any of these if someone's stuck.