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Overview

In this tutorial, you will set up a common booking workflow:
  • Send a booking confirmation email after a user completes a booking.
  • Send a recovery email if a user starts a booking but does not complete it in time.
By the end, you will have:
  • Two Custom Events (booking_started, booking_complete)
  • One Journey that branches on completion vs abandonment
  • A booking Data Feed for confirmation details
  • An optional coupon Data Feed for recovery incentives
This guide focuses on configuring OneSignal. Your booking system and backend can be implemented in any language or framework.

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Setup flow

  1. Your app tracks a booking_started custom event.
  2. This enters the user into a Journey.
  3. The Journey waits for a booking_complete event and if not received in time, it sends follow-up reminders.
  4. If the booking completes, OneSignal calls a booking Data Feed at send time and sends a confirmation email with the latest booking details.
  5. If the booking does not complete within the wait window, the Journey follows the expiration path and sends a recovery email.

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Setup

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Prerequisites

Before you begin, make sure you have:
  • A OneSignal app with the Email channel enabled
  • A backend endpoint that can return booking and/or coupon data as JSON
  • A stable user identifier shared between your app, backend, and OneSignals External ID
  • Access to Custom Events

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1. Track booking events

Track the following Custom Events. These can be from your app (using our SDK) or from your backend (using our REST API). Event names:
  • booking_started — when the user begins the booking flow
  • booking_complete — when the booking is successfully completed
Use the trackEvent() method on our Mobile SDK and/or Web SDK to send custom events directly from your app/website.
Example
OneSignal.User.trackEvent("booking_started");
OneSignal.User.trackEvent("booking_complete");
Use the same user identity when tracking events and when returning data from your backend. Mismatched IDs are the most common cause of missing personalization.

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2. Create Data Feed aliases

In OneSignal, go to Settings > Data Feeds and create the following aliases. Booking Data Feed: Use this feed to pull the latest booking details at send time.
  • Alias: booking_data
  • Method: GET
  • URL:
Example endpoint
https://your-domain.com/datafeed/booking?user_id={{subscription.external_id}}
Example response:
JSON
{
  "first_name": "Sam",
  "last_booking": {
    "service_type": "Consultation",
    "booking_date": "January 22, 2026",
    "booking_time": "2:00 PM",
    "price": 45
  }
}
Coupon Data Feed (optional): Use this optional feed if you want to include a coupon code in your recovery email.
  • Alias: coupon
  • Method: GET
  • URL:
Example endpoint
https://your-domain.com/datafeed/coupon?user_id={{subscription.external_id}}
Example response:
JSON
{
  "first_name": "Sam",
  "code": "PROMO8F3K2",
  "discount_text": "10%",
  "expires_in_hours": 2,
  "deep_link": "https://your-domain.com/checkout?coupon=PROMO8F3K2"
}
Secure your Data Feed endpoints. In production, send an API key in request headers (for example x-api-key) and configure that header in Settings > Data Feeds instead of embedding secrets in the URL.

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3. Create email templates

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Booking confirmation email:

Subject: 
Your booking details
Body: 
Hi {{ data_feed.booking_data.first_name | default: "there" }},

Thanks for your booking! Here are your appointment details:

Service: {{ data_feed.booking_data.last_booking.service_type }}
Date: {{ data_feed.booking_data.last_booking.booking_date }}
Time: {{ data_feed.booking_data.last_booking.booking_time }}
Price: ${{ data_feed.booking_data.last_booking.price }}

We look forward to seeing you!

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Booking recovery email

Subject: 
Complete your booking and save
Body: 
Hi {{ data_feed.coupon.first_name | default: "there" }},

Finish your booking in the next {{ data_feed.coupon.expires_in_hours }} hours and save
{{ data_feed.coupon.discount_text }} with this code:

{{ data_feed.coupon.code }}

Use it here:
{{ data_feed.coupon.deep_link }}
Always include default filters in Liquid to prevent blank content if a Data Feed field is missing.

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4. Build the Journey

  1. In OneSignal, go to Messages > Journeys > Create Journey
  2. Set the Entry Trigger to:
    • Custom Event: booking_started
  3. Add a Wait Until step:
    • Condition: Custom Event occurs
    • Event name: booking_complete
    • Maximum wait time: 10 minutes
    • Enable the expiration path
  4. Configure the branches:
    • Completed: Send booking confirmation email
      • Data Feed: booking_data
    • Expired: Send recovery email
      • Data Feed: coupon
The expiration branch allows you to handle abandonment without additional logic in your app. See:

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5. Test and verify

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Verify events

Trigger the custom events from your app or backend and confirm. In OneSignal, go to Analytics > Custom Events and confirm you see:
  • booking_started events appear for your External ID
  • booking_complete events appear for your External ID

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Verify Data Feeds

Manually call your Data Feed endpoints using a known user ID and confirm:
  • A 200 response is returned
  • All expected fields are present

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Verify emails

Send test messages from the Journey editor and confirm:
  • Booking emails contain real booking details
  • Recovery emails contain a valid coupon
  • No Liquid variables render empty
If personalization is missing, confirm that the user ID in the Data Feed request matches the user who triggered the Journey.

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Example: Data Feed implementation

This example shows a minimal Express implementation for booking confirmation and recovery Data Feeds. Your backend language, framework, and data source can differ as long as the JSON response shape matches your email templates.

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Booking Data Feed example

import express from "express";

const app = express();

function dataFeedAuth(req, res, next) {
  if (req.headers["x-api-key"] !== process.env.DATAFEED_API_KEY) {
    return res.status(401).json({ error: "Unauthorized" });
  }
  next();
}

app.get("/datafeed/booking", dataFeedAuth, async (req, res) => {
  const { user_id } = req.query;

  if (!user_id) {
    return res.status(400).json({ error: "Missing user_id" });
  }

  const booking = await getLatestBookingForUser(user_id);

  if (!booking) {
    return res.status(404).json({ error: "No booking found" });
  }

  res.json({
    first_name: booking.first_name,
    last_booking: {
      service_type: booking.service_type,
      booking_date: booking.booking_date,
      booking_time: booking.booking_time,
      price: booking.price
    }
  });
});

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Coupon Data Feed example

app.get("/datafeed/coupon", dataFeedAuth, async (req, res) => {
  const { user_id } = req.query;

  if (!user_id) {
    return res.status(400).json({ error: "Missing user_id" });
  }

  const coupon = await generateCouponForUser(user_id);

  res.json({
    first_name: coupon.first_name,
    code: coupon.code,
    discount_text: coupon.discount_text,
    expires_in_hours: coupon.expires_in_hours,
    deep_link: coupon.deep_link
  });
});

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Implementation guidelines

  • Keep responses fast (Data Feeds are called at send time)
  • Always return a predictable JSON structure
  • Use 404 when no data exists
  • Secure endpoints with an API key sent via request headers

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Common issues

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Email shows empty values

  • Data Feed returned 404
  • Field names changed in the JSON response
  • User identity mismatch

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Journey does not branch

  • booking_complete event not tracked
  • Event name mismatch (case-sensitive)
  • Event occurs outside the wait window

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Data Feed returns 401 or 403

  • Missing or invalid API key
  • Header not configured in the Data Feed settings

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Next steps

  • Add event properties (service type, price) for more advanced Journey conditions
  • Add additional recovery steps such as push or SMS reminders
  • Use Journey exit rules to prevent repeated recovery messages