Fill Cancelled Booking Slots via Waitlist Webhooks + SMS/WhatsApp

Instantly fill cancelled booking slots using waitlist webhooks (SMS/WhatsApp ready)

When a booking is cancelled, this n8n workflow automatically finds the best waitlist matches, sends offers immediately, and uses atomic “first reply wins” claim handling—then sweeps every 30 minutes to re-offer expired/declined slots until the waitlist runs out.

What this workflow does

• Receives cancelled slots via webhook: Your calendar system POSTs each freed slot to the first webhook URL. Invalid payloads are rejected cleanly with a 422 response.
• Ranks the waitlist for that exact slot: Treatment match counts most, then flexibility, then the person’s own priority score. The top three matches get offer messages at once.
• Records an “offer book”: Each offer round tracks who was offered, who declined, and when the round expires.
• Claims are handled atomically: Replies arrive at a second webhook. The claim guard ensures the first TAKE wins the slot; later takers receive a polite response. STOP marks the sender as declined and releases the slot immediately.
• Re-offers automatically with a 30-minute sweeper: Every 30 minutes, a sweeper finds expired or declined slots, excludes anyone already offered/declined, re-ranks remaining candidates, and sends the next offers. When the waitlist is empty, the slot closes as exhausted.
• Schedules itself: Runs on a 30-minute schedule and logs a summary of re-offered and exhausted slots.

Use cases

• Reduce revenue loss when clients cancel last-minute by filling the gap from a waitlist.
• Handle high-volume cancellations safely with “first reply wins” atomic claim logic.
• Keep messaging consistent by routing offers through your messaging webhook for SMS/WhatsApp delivery.

Technical details (n8n)

• webhook nodes for: cancelled-slot intake and claim-reply processing
• if and code nodes for payload validation, ranking, and atomic claim behavior
• schedule trigger for the 30-minute sweeper
• respond to webhook for immediate 422 rejections and reply outcomes
• sticky note nodes for workflow clarity/documentation

Setup

• Point your booking system cancellation event to the first webhook URL.
• Point your messaging webhook (SMS/WhatsApp sending) to the claim reply URL.