ALLIN – Intelligent Group Payments & Smart Settlement

Interactive Dashboard - Target Pool, Contributions, Settlements,etc
Financial Audit Ledger, Member Payments
New Group Creation, Joining
Deposit Money to New Group
New Expense Creation (inside a specific group)
New Expense Creation with AI bill parsing/ qr scanner
Expense Tracker for every group
Paypal Payment and Settlement of Outstanding Dues(in case of personal advance)
Transaction record of all members of the group
Profile

Inspiration

Imagine going on a trip with friends. One person pays for the hotel, another books the cab, someone else pays for dinner, and soon nobody remembers who owes whom. Splitting bills manually, tracking individual contributions, and chasing payments becomes frustrating.

We wanted to solve this everyday problem by building something more intelligent than a conventional expense-splitting application. Our vision was to make group payments transparent, automated, and effortless.

What it does

ALLIN is an AI-powered group payment and smart settlement platform that simplifies the entire lifecycle of shared expenses.

Group Management: Create groups and invite members through QR codes or PINs.
AI Receipt Scanner: Upload a receipt and use Gemini Vision to extract merchant details, individual items, prices, taxes, and totals.
Intelligent Expense Splitting: Assign individual items to group members and automatically calculate accurate contributions.
Smart Settlement: Track outstanding balances and identify who owes whom, simplifying group settlements.
Member Approvals: Allow members to review and approve their individual expense shares before payment.
PayPal Integration: Facilitate payments through PayPal, supporting order creation, authorization, capture, and payment tracking.
Transaction Tracking: Maintain payment records and update transaction statuses through asynchronous payment events and webhooks.

How we built it

We built ALLIN using the MERN stack, with React for the frontend, Node.js and Express.js for backend APIs, and MongoDB for persistent data storage.

We integrated PayPal for payment processing, enabling users to participate in a structured group payment workflow. Webhooks help the backend receive payment events independently of frontend redirects.

For our AI-powered receipt scanner, we integrated Google's Gemini Vision API through the backend. It extracts structured information from receipt images, which users can review and edit before assigning items to group members.

We implemented deterministic expense-splitting logic using integer-based currency calculations to maintain accuracy and avoid floating-point rounding errors.

The backend also uses MongoDB transactions and event-driven processing to coordinate data updates and payment-related workflows.

Challenges we ran into

Financial Accuracy: Ensuring that individual expense shares always add up exactly to the original bill, including taxes and tips.
AI Reliability: Converting unstructured receipt images into accurate, structured data while handling missing or incorrectly extracted information.
Payment Lifecycle Management: Handling asynchronous PayPal events and keeping payment statuses consistent between the payment provider and our database.
Frontend-Backend Integration: Integrating new AI functionality into existing expense workflows without disrupting established features.
State Management: Coordinating expense creation, member approvals, and payment status transitions.

Accomplishments that we're proud of

Building an end-to-end group payment platform rather than just another bill-splitting calculator.
Integrating AI-powered receipt intelligence directly into the expense creation workflow.
Implementing item-level expense allocation with accurate monetary calculations.
Integrating PayPal payment authorization, capture, and payment tracking.
Developing a smart settlement feature that makes outstanding group balances easier to understand.
Creating a unified workflow connecting receipt scanning, expense management, approvals, and payments.

What we learned

Building ALLIN taught us that financial applications require much more than basic CRUD operations. We gained practical experience with payment gateway integration, asynchronous communication, webhook handling, database transactions, and financial data consistency.

We also learned how to integrate vision-based AI into an existing application while maintaining deterministic business logic for all monetary calculations.

Most importantly, we learned how to design and integrate multiple independent components into a cohesive application.

What's next for ALLIN – Intelligent Group Payments & Smart Settlement

We envision taking ALLIN further by introducing intelligent spending insights, more advanced settlement optimization, stronger payment recovery mechanisms, and enhanced transaction reconciliation.

Our long-term goal is to make group payments more transparent, reliable, and effortless, regardless of the size or complexity of the group.