Case Study

Mobile

Invoice Factory – Invoice Hub & QR Code Management System

Invoice Factory is a comprehensive and intelligent e-Invoice management platform specifically designed for Malaysian businesses to comply with LHDN (Lembaga Hasil Dalam Negeri) MyInvois regulations. The application empowers suppliers and business owners to seamlessly create, manage, submit, and track digital invoices in real-time while ensuring full compliance with Malaysia’s national e-invoicing standards. With built-in QR code scanning capabilities, digital signature support, and multi-platform authentication, Invoice Factory provides a complete end-to-end invoicing solution. The system bridges the gap between businesses and the Malaysian tax authority by automating the invoice submission process, reducing manual errors, and providing instant status tracking — all from a single unified platform accessible on both Android and iOS devices.

Flutter

Firebase + Custom REST API

SQLite

Cloud Firestore

GetX MVC Pattern with Real-time Sync

RSA Digital Signing + AES/CBC Encryption

Invoice Factory – Invoice Hub & QR Code Management System screen 1

Invoice Factory – Invoice Hub & QR Code Management System screen 2

Invoice Factory – Invoice Hub & QR Code Management System screen 3

Invoice Factory – Invoice Hub & QR Code Management System screen 10

Invoice Factory – Invoice Hub & QR Code Management System screen 11

Challenges & solutions

The technical problems our team solved to ship a reliable, unified mobile experience.

Generating valid UBL 2.1 XML invoices required strict schema compliance, XML canonicalization, RSA-SHA256 digital signatures, and XAdES-BES signing using PKCS#12 certificates, where even minor formatting errors resulted in invoice rejection.

Designed a two-stage XML generation pipeline that first creates the unsigned UBL document, then generates cryptographic digests, applies RSA-SHA256 digital signatures, and embeds XAdES signature blocks, producing fully compliant invoices accepted by LHDN validation services.

LHDN processes invoices asynchronously, returning only an acknowledgement while validation occurs later, making it difficult to keep local invoice status synchronized with official processing results.

Built a multi-stage submission pipeline that uploads signed invoices, stores intermediate identifiers, automatically polls validation endpoints after submission, and synchronizes local records with official invoice status and long IDs.

The MyInvois API enforces strict rate limits, and fixed retry strategies frequently retried too early or unnecessarily delayed requests during high server load.

Developed a dynamic retry mechanism that extracts server-provided retry intervals from HTTP 429 responses and automatically retries requests after the recommended wait period, greatly improving API reliability during peak usage.

Expired OAuth tokens caused failed requests, while concurrent refresh attempts introduced race conditions and inconsistent authentication states.

Implemented a Dio interceptor with a single-refresh locking mechanism that transparently renews expired tokens, retries failed requests, and gracefully handles session expiration without interrupting the user experience.

Continuous camera frames overloaded barcode processing, while rotated gallery images frequently failed QR code detection.

Introduced frame-locking to prevent concurrent scan operations and implemented automatic image rotation across multiple orientations, significantly improving QR recognition accuracy while maintaining smooth camera performance.

Traditional SQLite migrations became difficult to maintain as database models evolved, while loading large datasets degraded application performance on mobile devices.

Built a dynamic database engine capable of automatically creating tables, safely migrating schemas, and performing paginated queries, enabling reliable offline-first functionality with minimal maintenance effort.

Google, Apple, Huawei, and Firebase authentication each required different security models, token handling, and platform-specific implementation details while maintaining a consistent user experience.

Integrated multiple authentication providers into a unified login architecture with secure Apple nonce generation, Huawei support, Firebase authentication, and centralized session management.

Android Scoped Storage and iOS sandbox restrictions required different file management strategies, while incomplete file writes occasionally produced corrupted PDF documents.

Developed a platform-aware PDF generation and file management system that handles storage differences, verifies completed writes, and supports reliable viewing, downloading, printing, and sharing across Android and iOS.

Authentication tokens and confidential user information required secure local storage without compromising usability, particularly when supporting "Remember Me" functionality.

Implemented AES-256 encryption for sensitive data and designed a controlled storage management system that securely clears session information during logout while preserving user preferences when appropriate.

Key features

What users get in the finished, shipped product.

Dashboard and Overview :

Overview : Centralized home screen for daily activity and statistics
Insights : Real-time tracking of total, draft, and submitted e-Invoices
Monitoring : Quick-access recent history with instant status indicators

Invoice Management :

Control : Support for multiple types including Credit and Debit Notes
Tracking : Automated status updates from Draft to LHDN Submission
Organization : Structured history with official receipt number management

QR Code Scanner :

Scanning : Real-time detection powered by Google ML Kit with flash control
Processing : Auto-populates scanned data for instant review and verification
Efficiency : Seamless camera-to-form workflow with manual entry fallback

E-Invoice Submission (LHDN MyInvois) :

Compliance : Automatic UBL XML generation with secure P12 digital signing
Integration : Direct connection to Malaysia’s national MyInvois API
Tracking : Real-time submission status and direct cancellation support

Supplier and Buyer Management :

Onboarding : Guided 3-step setup for TIN, MSIC codes, and business details
Database : Centralized master records for buyers and tax information
Efficiency : Instant population of contact details during invoice creation

Item / Product Management :

Overview : Master catalog for all billable products and services
Tracking : Pre-configured pricing, tax types, and classifications
Speed : One-tap item selection to auto-fill line details in new invoices

Multi-Provider Authentication :

Options : Secure login via Google, Apple, and Huawei Sign-In
Security : Robust Firebase backend for session and token management
Control : Reliable user account lifecycle and data deletion support

PDF Generation and Sharing :

Output : Professional PDFs featuring logos and itemized tax breakdowns
Sharing : Instant distribution via Email, WhatsApp, or native apps
Branding : Clean, formatted templates designed for business compliance

Data Security and Encryption :

Protection : AES/CBC encryption with PKCS7 padding for local storage
Compliance : RSA digital signing for LHDN-standard legal submissions
Reliability : Enterprise-grade security for sensitive financial records

Responsive UI and User Experience :

Design : Modern interface with customizable supplier branding
Navigation : Smooth bottom tab bar transitions and intuitive workflows
Feedback : Real-time toast notifications for instant user confirmation

Tech integrations

Third-party SDKs & libraries

6 core integrations powered

Firebase

Core system integration

Google ML Kit

Core system integration

Google Sign-In

Core system integration

Sign in with Apple

Core system integration

Huawei Account

Core system integration

MyInvois LHDN API

Core system integration

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