n8n Workflow: Fill Cancelled Appointments via Waitlist (Sheets, Calendar, Twilio)

Instantly fill cancelled appointments from your waitlist—automatically

This n8n workflow watches your Google Sheets appointments for cancellations, then texts waitlist candidates via Twilio with a one-tap confirmation link to claim the newly opened slot. If someone confirms within 20 minutes, it books them in Google Calendar and updates both Google Sheets tabs—otherwise it moves on, or notifies the owner if the slot can’t be filled.

What this workflow does

• Monitors cancellations in Google Sheets: Polls the Appointments tab every 5 minutes and processes updated rows.
• Normalizes appointment timing: Converts Google Sheets date/time serial values into ISO date/time strings and calculates a 30-minute end time.
• Triggers only for “Cancelled” slots: Continues only when the appointment status is Cancelled and the row has not been marked as waitlist-processed (then flags it as processed in Sheets).
• Iterates through matching waitlist candidates: Searches the Waitlist tab for entries in a Waiting status that match the cancelled appointment’s service type, offering candidates one-by-one.
• Offers the slot via Twilio SMS: Marks each candidate as Offered, sends an SMS with a confirmation link, and waits up to 20 minutes for the link to be opened.
• Books on confirmation: If confirmed, creates the event in Google Calendar, appends a new Filled - Waitlist row in Appointments, updates the waitlist entry to Booked, and sends a final Twilio confirmation SMS.
• Expires and escalates: If not confirmed in time, marks the candidate as Expired and tries the next. If no one confirms, marks the original appointment Cancelled - Unfilled and texts the owner via Twilio.

Use cases

• Clinics, tutoring services, salons, or any business with recurring appointment slots and a waitlist
• Reducing downtime from cancellations by rapidly filling open times
• Operators who want an n8n-driven, spreadsheet- and calendar-based scheduling workflow

Technical details

• Google Sheets: Reads and updates Appointments and Waitlist tabs
• Google Calendar: Creates the confirmed appointment event
• Twilio: Sends SMS messages and handles one-tap confirmations with a 20-minute wait window
• n8n nodes/logic mentioned: if, code, wait, filter, twilio, sticky note