n8n Workflow: Auto-Fill Cancelled Appts from Google Sheets Waitlist

Automatically re-offer cancelled appointment slots to your waitlist—every 15 minutes

This n8n workflow finds cancelled appointments in your Google Sheets and automatically sends time-limited slot-offer emails to the best-matching clients from your Waitlist, updating both sheets and notifying staff of delivered, failed, and data-quality issues.

What this workflow does

Designed for reliable waitlist fulfillment, the workflow runs on a 15-minute schedule and performs these steps:

• Validates setup: checks that required settings are present and that the Google Sheets tabs include the expected column headers for both Bookings and Waitlist.
• Matches cancelled slots to eligible clients: reads both tabs, identifies cancelled appointments that meet your notice / ahead-of-time rules, and selects the longest-waiting eligible clients based on service and date range.
• Writes offer status to Sheets: updates the chosen waitlist rows with an offered status and offer metadata, and updates the corresponding booking rows.
• Sends slot-offer emails via Gmail: delivers time-limited offers using the Gmail node, with optional routing of emails to staff in test mode.
• Tracks delivery results: confirms successful Gmail delivery or rolls back waitlist updates as needed; marks recipients as send failed for undeliverable emails.
• Notifies staff: emails a summary of offers sent and any delivery failures, plus a once-per-day report of malformed or duplicate rows that are skipped.

Use cases

• Fill gaps when a client cancels—without manual outreach.
• Offer cancelled time slots to the longest-waiting eligible clients by service and availability windows.
• Improve data quality by automatically flagging malformed/duplicate waitlist or booking rows.

Technical details

• Schedule: runs every 15 minutes
• Integrations / nodes: Google Sheets (Bookings + Waitlist tabs), Gmail, plus set, code, sticky note, http request, and error trigger

If you’re an n8n user, automation engineer, or SaaS operator managing appointment capacity, this workflow helps you maximize rebooking while keeping your data and communications consistent.