Mobile App for Electronic Queues: Eliminate Waiting Chaos

When a visitor steps away from the queue and misses their call, the entire system stalls. Operators waste time reassigning tickets, and throughput drops. A mobile app with real-time synchronization solves this: tickets update instantly via WebSocket, and personalized push notifications alert users when they are 3, 2, or 1 position away. In one of our projects for a regional MFC with 15 windows and 2,000 daily visitors, idle time dropped by 40% (from 8 minutes to 4.8 minutes per visitor), and operator time spent on re-assignments fell by 20%.

Technical Challenges We Solve

WebSocket vs SSE vs Polling

The core challenge is keeping the queue state in sync without overwhelming the server. We use WebSocket for bidirectional, low-latency communication. With a persistent connection, the server pushes events as soon as a number is called. On Flutter, we use web_socket_channel and manage state via Riverpod StreamProvider or BLoC. WebSocket delivers updates in under 100 ms — three times faster than SSE and orders of magnitude faster than polling.

Background App and Push Notifications

When the app goes to background, the WebSocket closes. To avoid missed calls, we implement a two-tier notification system:

• "3 people ahead of you" — forewarning.
• "Your number is next!" — time to approach.
• "You are being called to window 5" — immediate action.

Pre-booking and Reminders

Advanced scenario: users book a specific time slot. The server (using Bull Queue on Redis) schedules push reminders 30 minutes and 10 minutes before the slot. This reduces no-shows by 35%, as seen in our medical center deployments.

Our Approach: Building a Reliable Queue System

Stack and Architecture

• Backend: Node.js + PostgreSQL + Redis + Bull Queue
• Mobile: Flutter (or React Native) with single codebase for iOS and Android
• Push: FCM + APNs with personalized targeting
• CI/CD: Fastlane + Shorebird for over-the-air updates

Case Study: MFC Deployment

A large MFC with 20 windows and 3,000 daily visitors needed to reduce chaos. We built a Flutter app with WebSocket sync and push notifications. Key metrics after launch:

• Average wait time per visitor: from 12 minutes to 7 minutes (41% reduction)
• Missed calls: from 18% to 4% (78% reduction)
• Operator overhead: cut by 22% due to automated call management

The system handled 5,000 concurrent WebSocket connections without degradation.

How We Work: From Discovery to Launch

1. Analysis: Study visitor flow, number of windows, service types, user scenarios.
2. Design: Architecture for queue management (in-memory Redis queue), API schemas, UI mockups.
3. Implementation: Backend on Node.js + PostgreSQL, mobile on Flutter, push notification setup.
4. Testing: Load testing up to 1,000 concurrent users; usability testing.
5. Deployment: CI/CD pipeline, app store submission, monitoring (Crashlytics).

Contact us to discuss your project and get a preliminary estimate.

Timeline Estimates

Common Mistakes to Avoid

• Ignoring background state: Without push fallback, users miss calls. Our system ensures WebSocket and push work in tandem.
• Using polling under high load: Polling at 5-second intervals on 5,000 clients generates 1,000 requests/second. We use WebSocket to reduce server load by 90%.
• Not testing with realistic concurrency: We simulate peak loads to guarantee stability.

What's Included in the Development?

• Mobile app (iOS + Android) and backend service
• Integration with existing systems (e.g., MFC management software)
• Push notification setup (FCM + APNs)
• QR code generation and scanning for tickets
• Admin analytics dashboard (visitor count, average time, peak loads)
• API and architecture documentation
• Staff training on admin panel
• 3 months of post-launch support

Push Notifications in Mobile App: APNs, FCM, Segmentation, Rich Push

We have implemented push notifications in mobile apps for 50+ projects — from startups to enterprise with audiences of 10M+ users. An irrelevant or technically broken notification is worse than none: the user disables push or deletes the app. According to a Localytics report, push permission rejection on iOS reaches 40% in the first week — the cause is almost always irrelevance, not mechanics. Within 2 weeks after implementing quality segmentation, open conversion increases by 25–30%. Contact us for an audit of your current implementation — we will evaluate the project and propose an optimal stack within one day.

How the Infrastructure Works: APNs and FCM

APNs is the only delivery channel on iOS. Everything else (OneSignal, Braze, Airship) is a wrapper on top of it. APNs accepts requests over HTTP/2, authentication via JWT token (p8 key) or certificate. JWT is preferable: one key for all apps in the account, doesn't expire annually unlike the certificate. For more details, see the official documentation.

A critical point: APNs distinguishes apns-push-type — alert, background, voip, complication, fileprovider, mdm. An incorrect type on iOS 13+ causes background notifications not to wake the app. We've seen projects where content-available: 1 was sent without apns-push-type: background — the app didn't receive silent push on some devices, and the team spent a month looking for an 'app bug'.

FCM on Android works through Google Play Services. For devices without GMS (Huawei, part of the Chinese market), Huawei Push Kit or a direct WebSocket is needed — a separate task. FCM supports data messages (handled in onMessageReceived) and notification messages (the system displays automatically if the app is in the background). Mixing them requires caution: if the notification block has a click_action but the deep link is not registered in the app, tapping the notification simply opens the main screen without navigation.

Why Segmentation Is the Foundation of Effective Push Notifications?

Sending to everyone indiscriminately quickly exhausts user loyalty. Personalized messages are clicked 3 times more often than bulk ones, and proper segmentation reduces churn by 25% (on one project it brought significant additional revenue per quarter). The cost of setting up segmentation in OneSignal or a custom backend depends on the complexity of filters.

Proper segmentation is built on several levels.

Topics are for broad categories: 'new promotions', 'order status updates'. User subscribes via FirebaseMessaging.getInstance().subscribeToTopic("orders"). Simple, but no flexible filtering.

Attribute-based segments — via OneSignal, Braze, or custom backend. We store in the user profile: language, device type, last activity, LTV segment. Notification goes only to those with last_active < 7_days and plan = premium. OneSignal allows building such filters in the interface without code.

Personalized — by specific device_token. It's important to store tokens correctly: the token updates on app reinstall, restoration from backup on a new phone, or resetting settings. On iOS, use UNUserNotificationCenter + didRegisterForRemoteNotificationsWithDeviceToken, save to backend on every launch, not just the first. Otherwise, after 3 months 30% of tokens in the database are outdated.

What Is Rich Push and How Does It Boost Conversion?

A standard notification with title and text is clicked less often than a rich push with image and action buttons — by 3 times. But implementing rich push is a separate task on each platform.

On iOS, rich content requires UNNotificationServiceExtension (to modify payload) and UNNotificationContentExtension (custom UI). The extension runs in a separate process with limited time and memory. If the extension crashes or exceeds the timeout, the system shows the original payload without media. A typical mistake is trying to load an image over HTTP (not HTTPS): ATS blocks the request, the extension silently fails, and the user sees a notification without an image.

On Android with API 26+, notifications are tied to NotificationChannel. If the channel is created with IMPORTANCE_LOW, sound and vibration are unavailable. Different notification types (transactional, marketing) should be in different channels so the user can disable marketing without losing order notifications. BigPictureStyle, MessagingStyle, InboxStyle are templates for expanded notifications. MessagingStyle with Person and avatars is the best choice for chats.

How to Track Delivery and Conversion of Push Notifications?

Sending a notification is half the work. It's important to know: was it delivered, opened, and did it lead to a target action.

FCM returns a MessageId on send, but does not guarantee a delivery callback — by design. For open tracking, custom logic is needed: on notification tap in onMessageReceived or via getInitialNotification() / onNotificationOpenedApp (OneSignal SDK), send an event to analytics with notification_id.

OneSignal provides built-in delivery and CTR analytics. For more detailed analysis — integrate with Amplitude or Mixpanel via webhook on open events. The budget for such a dashboard varies depending on event volume.

How We Implement Push Notifications: Typical Process

1. Audit current implementation — check token storage, update handling, notification types.
2. Design architecture — choose transport (FCM + APNs), segmentation layer (OneSignal/Braze/custom), personalization method.
3. Implementation — write registration code, inbound handling, rich push, deep linking.
4. Testing — send test campaigns, verify delivery on different devices, simulators, regions.
5. Monitoring and analytics — set up dashboard, open and conversion events.
6. Documentation and training — hand over operational materials to the team.

Typical stack: FCM + APNs at transport level, OneSignal or Firebase Notifications Composer for segmentation, custom backend for personalized event-based notifications. For large apps with >1M users, OneSignal has pricing limits — then we use Braze or a custom implementation on AWS SNS.

Timelines depend on complexity: basic FCM+APNs integration with transactional notifications — 1–2 weeks. A full system with segmentation, rich push, analytics, and A/B testing — 4–8 weeks. Order an audit of your current push infrastructure or get a consultation on implementing push notifications in your mobile app — we will contact you within a day and provide an accurate estimate.