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Event ticketing backend: auto QR tickets with Google Sheets & Gmail

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Created by: Khairul Muhtadin || khmuhtadin
Khairul Muhtadin

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Last update 3 days ago

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Ticketing Backend automates registration, QR-ticket generation, email delivery, and check-in validation using Google Sheets, Gmail, and a webhook scanner — reducing manual ticket prep from ~3 hours to under 5 minutes for 200 attendees.

Screenshot 20251005 at 15.01.48.png

Last updated: September 2026.

Why Use This Workflow?

  • Time Savings: Automates ticket generation & delivery. reduces manual processing for 200 attendees from ~3 hours to <5 minutes.
  • Cost Reduction: Removes dependency on paid ticketing platforms for basic events — save up to $150–$300/month for small organizations.
  • Error Prevention: Single-source truth in Google Sheets with QR-based check-in reduces double-checkin and human errors by >90%.
  • Scalability: Runs on a schedule and webhooks; scales from dozens to thousands of tickets (watch API/email quotas).

Ideal For

  • Event Organizers / Community Managers: Sell & distribute tickets for meetups, runs, and local events with immediate QR delivery.
  • Operations / Venue Staff: Fast, reliable check-in via mobile scanner POSTing to webhook for instant validation.
  • Small Agencies & SaaS Teams: Lightweight, low-cost ticketing backend that integrates with existing Google accounts.

How It Works

  1. Trigger (Registration): POST /v1/register receives registration payload (nama, email, no_hp, jumlah_tiket, total_price, payment_method).
  2. Data Collection (Registration): Validate input → check existing participant in Register sheet → append registration.
  3. Processing (Ticket Generation): Scheduled job (START runs every minute) finds rows with Payment Status = PAID and Email Sent = NO.
  4. Intelligence Layer: For each ticket: generate unique Ticket ID (TL-YYYYMMDD-XXXX-N-HASH), build QR payload JSON, create QR image via qrserver API, and build HTML email with embedded base64 QR.
  5. Output & Delivery: Send ticket email(s) via Gmail; write one Tickets row per generated ticket and mark Email Sent = YES in Register.
  6. Storage & Logging: All participant & ticket records persisted to Google Sheets; check-in events update row (Checked In = YES and Checkin Time).

Core Endpoints

  • Registration webhook: POST /v1/register
  • Scanner webhook (check-in): POST /v1/scanner

Event Metadata

  • Event: TABRAK_LARI
  • Event date: 15 November 2025
  • Event location: GOR Pontianak

Setup Guide

Prerequisites

Requirement Type Purpose
n8n instance Essential Host the workflow and webhooks
Google account (Sheets + Gmail) Essential Store tickets & send emails
Google Sheet Essential Register & Tickets data store
Public webhook URL / reverse proxy Essential Expose /v1/register & /v1/scanner to scanners/clients
qrserver.com (public API) Optional Generate QR images (no credentials)

Important: Make sure your n8n instance URL is publicly accessible or use a tunneling/reverse proxy so webhooks can receive POSTs.

Installation Steps

  1. Import the JSON into your n8n instance.
  2. Configure credentials:
    • Google Sheets OAuth2: Grant access to Google Drive & Sheets API (spreadsheets.readonly & spreadsheets).
    • Gmail OAuth2: Grant send email scope (Gmail send).
  3. Update environment-specific values:
    • Verify Google Sheet ID.
    • Set the public base URL for ticket scanner clients to POST /v1/scanner.
  4. Customize settings:
    • Event name/date/location (variables in Generate Ticket Data / Build HTML Email).
    • Email sender address and subject line in Gmail node.
  5. Test execution:
    • Use a sample POST to /v1/register with valid fields to create a registration.
    • Mark a row as PAID and Email Sent = NO to trigger scheduled ticket generation.
    • Simulate a scanner POST to /v1/scanner with the barcode JSON payload to test check-in.

Technical Details

Core Nodes

Node Purpose Key Configuration
REGISTER (Webhook) Accepts registration POSTs Path: /v1/register
Validate Input (Code) Server-side validation Validates nama, email, no_hp, jumlah_tiket, payment_method
Get Participant (Google Sheets) Check duplicate email Filters Register tab by Email
Store Data (Google Sheets) Append registration Tab: Register (gid=0)
START (Schedule Trigger) Finds paid registrations Runs every 1 minute
Get Rows (Google Sheets) Reads Register rows Reads full Register tab
Filter Paid Not Sent (Filter) Finds rows with Payment Status=PAID & Email Sent=NO Filter node conditions
Generate Ticket Data (Code) Generate ticket IDs & QR payloads Ticket ID format TL-YYYYMMDD-XXXX-N-HASH
Generate QR Code (HTTP Request) Calls qrserver.com to build PNG URL: https://api.qrserver.com/v1/create-qr-code/?size=300x300&data=...
Build HTML Email (Code) Builds ticket HTML & embeds Base64 QR Template contains ticket details & QR
Send Email (Gmail) Sends ticket email To: recipient Email; Subject configurable
Update Sheet (Tickets) Append ticket rows Tab: Tickets (gid=2010454173)
Parse Data (Code) Aggregates ticket IDs per email Updates Register with combined ticket IDs
SCAN TICKET (Webhook) Check-in endpoint Path: /v1/scanner
Parse Barcode (Code) Parses incoming scanner payload Expects JSON in body.barcode
Get Tickets (Google Sheets) Lookup ticket by Ticket ID Filters Tickets tab by Ticket ID
Ticket Available? (If) Validates existence & Checked In status Branches to update or return error
Update Ticket Status (Google Sheets) Mark Checked In = YES Sets Checkin Time to scannedAt
Checked IN / Already Checked IN (RespondToWebhook) Respond payloads for scanner JSON responses with status & metadata

Workflow Logic

  • Registration: Writes to Register sheet. A scheduled job picks up PAID rows where Email Sent = NO; for each row it generates one record per ticket, calls the QR API for an image, sends an email per ticket (multi-ticket support), then appends Tickets rows and marks Email Sent = YES by updating the Register sheet with combined ticket IDs.
  • Check-in: The scanner webhook accepts barcode JSON, extracts ticket_id, looks up the Tickets sheet, prevents duplicate check-ins by checking "Checked In" flag, and updates sheet with check-in timestamp on success.

Customization Options

Basic Adjustments

  • Email Template: Edit Build HTML Email node to change branding, copy, or layout.
  • Ticket ID Format: Change code in Generate Ticket Data to alter prefix or hash length.
  • Event Metadata: Change event_name, event_date, event_location in code nodes.

Advanced Enhancements

  • Payment Gateway Integration: Integrate with payment gateway (e.g., webhook from Stripe) to automatically set Payment Status = PAID — complexity: medium.
  • Cloud Storage for QR Images: Use cloud storage (S3) for QR images instead of base64-embedding — complexity: medium-high.
  • Batch Email Provider: Use batch email provider (SendGrid/Mailgun) for high-volume events to reduce Gmail quota risks — complexity: medium.

Troubleshooting

Problem Cause Solution
Invalid QR / scanner returns "Invalid QR code format" Scanner payload not sending barcode JSON or malformed JSON Ensure scanner POST body contains valid JSON string under body.barcode; validate payload in Parse Barcode node
Ticket exists but cannot update Google Sheets API auth / permission error Reconnect Google Sheets OAuth2 credential; ensure the service account/user has edit access to the sheet
Emails not sent Gmail OAuth2 credential missing or Gmail API quota reached Reauthorize Gmail credential; consider switching to SendGrid/Mailgun for large volumes
Duplicate check-in allowed Logic checking "Checked In" value mismatch (case/format) Normalize the Checked In field values and use strict comparisons in Ticket Available? node
Slow generation for many tickets Sequential QR calls and sends Use parallel execution or a dedicated email service; increase worker resources for n8n instance

Use Case Examples

Scenario 1: Community Fun Run (200 attendees)

  • Challenge: Manual QR generation and emailing takes ~3 hours.
  • Solution: After marking registrations as PAID, the scheduled job generates 200 QR tickets and emails them automatically.
  • Result: Ticket prep completed in <5 minutes; volunteer time reduced by ~3 hours.

Scenario 2: Regional Festival (2,000 tickets)

  • Challenge: High volume requires reliable delivery and check-in speed.
  • Solution: Use this workflow but replace Gmail with a transactional email provider (SendGrid) and host n8n on a scalable instance. Monitor Google Sheets and email provider quotas.
  • Result: Automated delivery scales; on-site check-in handled via the /v1/scanner endpoint with near-instant validation.

Quick Answers

How do tickets get generated?
Mark registrations as PAID with Email Sent = NO. The scheduled job runs every minute, generates QR tickets, and emails them.
How does check-in work?
The scanner POSTs barcode JSON to /v1/scanner. The sheet validates the ticket and marks Checked In.
What about quotas at scale?
Watch Gmail and Google Sheets API quotas. For high volume, swap in SendGrid or Mailgun.

Additional Information

Made by: khmuhtadin
Category: Event Automation, Ticketing Backend
Tags: google-sheets, gmail, qr-code, webhook, ticketing

Need custom workflows or help adapting this for your event? Contact me

Note: Import the JSON into your n8n instance to get started.

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Additional info

Built with n8n. Need an assessment on your business? Feel free to reach out at https://khmuhtadin.com/consultation/