WhatsApp Business API Automation in n8n: Start With the Window

Description and use

Automating WhatsApp replies with n8n while respecting the 24‑hour service window, verifying Meta signatures, deduplicating messages, and using human review for AI drafts.

Problem

Small businesses receive hundreds of WhatsApp messages and answer them manually; they need automated replies that respect WhatsApp’s rules and cost structure.

Outcome

An n8n workflow that respects WhatsApp’s 24‑hour window, avoids duplicate replies, and uses human review for AI‑drafted messages, reducing manual effort while staying compliant.

Workflow

• Receive message via webhook
• Verify Meta signature using app secret
• Deduplicate by storing message_id in Postgres
• Determine message type (FAQ or human handoff)
• If FAQ, draft reply from fixed source
• Send draft to human for approval via WhatsApp
• If approved, send final message to customer

Evidence

The single most useful fact about the platform is the customer service window. According to the WhatsApp Business Platform pricing page, when a user messages a business it opens a 24-hour window in which the business can reply with service messages at no charge, and the window resets with each new user message.

Source

First, verify that the request came from Meta. Incoming requests carry a signature header you can check against your app secret.

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Second, deduplicate. If your workflow is slow and the sender decides it hasn't heard back, you can see the same message twice. I store each message ID in a small Postgres table and skip anything already seen.

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