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Case Study: Building a Dining App to Split Bills and Send Group Invoices in 7 Days

iinvoices

2026-02-03

10 min read

How a seven-day micro-app sprint produced a dining app that splits bills and sends group invoices—practical blueprint for freelancers.

Hook: Hate chasing payments after a group dinner? Build a bill-splitting app in a week.

Slow payments and messy expense splits are a hidden tax on every freelancer and small business owner. One missed payment, a confused group chat, or a manual reconciliation can cost hours and harm cash flow. Inspired by Rebecca Yu's seven-day micro-app sprint, this case study shows how a solo maker prototyped a dining app that splits bills and sends group invoices in 7 days—using AI copilots, no-code primitives, and modern payment rails. If you want a repeatable, low-cost blueprint to reduce DSO and automate group billing, read on.

The brief: What we built and why it matters in 2026

The goal was simple and tightly scoped: ship a minimal, secure web app that lets a host create a bill, split items or totals among participants, generate a consolidated group invoice, and accept payments (cards + ACH + instant rails where available). The constraint: build a working prototype in 7 days with no large engineering team.

Why this matters now: by late 2025 and into 2026, four forces changed the economics of rapid prototyping:

AI-assisted coding (vibe coding) matured—LLMs like ChatGPT and Claude can scaffold full-stack routes and workflows in minutes.
No-/low-code building blocks (Airtable, Supabase, Stripe, Gluon UIs, and Retool templates) accelerated integration work.
Real-time payment rails (FedNow, RTP, and expanded instant settlement by global processors) reduced settlement friction for group payments.
Embedded finance and improved APIs from Stripe, Plaid, and banking partners made onboarding and reconciliation easier for small businesses.

Core features (MVP)

Create a bill: Add items, taxes, tips, and total.
Split logic: Equal split, itemized split, or custom shares.
Group invoice: Generate one consolidated invoice with line-item breakdowns per payer and a master invoice for the organizer.
Payment collection: Allow each participant to pay via card, bank transfer (ACH), or instant pay where supported.
Notifications & receipts: Send email/SMS links and store receipts for tax and accounting export.

Tech stack and tools used (fast, reliable, low-cost)

The choices below prioritize speed, security, and small-business accounting needs. This is the stack used to prototype the dining app in seven days.

Frontend: SvelteKit (fast scaffolding, tiny bundles) + Tailwind for UI.
Backend / Database: Supabase (Postgres) for storage, auth, and functions—reduced backend boilerplate.
Payments: Stripe for card payments and ACH; Stripe Connect for splitting fees; native instant payout support when available.
Auth: Clerk or Supabase Auth with WebAuthn for passwordless sign-in (improves conversion for quick flows).
AI Assistants: ChatGPT (OpenAI) and Claude (Anthropic) for generating endpoints, test cases, and UX copy—used as coding copilots.
No-code integrations: Airtable for quick admin dashboards and Zapier / Make for notifications and lightweight automation.
Hosting / Deployment: Vercel for front-end, Supabase edge functions for server logic.
Monitoring: Sentry for error monitoring and Postgres analytics for usage metrics.

Why these tools? (a freelancer’s perspective)

For freelancers the priorities are time-to-first-value, predictable costs, and easy maintenance. Supabase gives a managed Postgres with auth so you avoid server management. Stripe handles all the tricky payment compliance and payout orchestration; using Stripe Connect or PaymentIntents reduces risk when splitting funds. AI copilots accelerate code generation—ask for a working API route and get back a function you can test.

Day-by-day 7-day build narrative

Below is a condensed daily log modeled on the micro-app sprint approach. The idea: focus each day on one deliverable and integrate continuously.

Day 0 — Define the MVP and UX flows (2 hours)

Write the acceptance criteria: “Organizers can create a bill and invite participants; participants receive a payment link; organizer sees reconciliation.”
Create wireframes (Figma) and a simple schema (bills, items, participants, payments).
Decide payment rails: Stripe PaymentIntents + ACH + optional instant payouts.

Day 1 — Backend schema and auth

Provision Supabase project and create tables: bills, items, participants, invoices, payments, receipts.
Enable Supabase Auth (OAuth + email magic links) for quick onboarding.
Use ChatGPT to generate table SQL and edge function scaffolds.

Day 2 — Frontend scaffolding and bill creation

Scaffold SvelteKit app, add pages for bill creation, item entry, and preview.
Wire in Supabase auth and simple CRUD for bills.
Build a reusable split algorithm (equal/itemized/custom) that returns per-person totals and line items.

Implement invoice generation: combine participant subtotals into CSV/JSON and create a master invoice record.
Generate short shareable links (secure tokens) that let invited payers open their invoice without full signup.
Prototype email/SMS send via SendGrid/Twilio (or Zapier + Gmail) for notifications.

Day 4 — Integrate payments

Integrate Stripe PaymentIntents on the participant-side: each share becomes a PaymentIntent or a separate PaymentLink.
Implement webhook processing for payment succeeded/failed events and reconcile to the invoice record (see automation patterns in prompt chains).
Test partial payments and tip capture.

Day 5 — Edge cases, refunds, receipts, tax handling

Add partial payment flows: allow a participant to pay partial amounts and re-open invoices.
Implement refund logic and a simple dispute flag for the organizer.
Auto-generate receipt PDFs and attach them to the invoice record for download and tax reporting. Keep storage costs low with best practices from storage optimization guides.

Day 6 — UX polish, branding, and testing

Polish UI copy with the help of an LLM (clear CTAs: “Pay your share” etc.).
Run user tests with 5 friends—fix confusing flows immediately.
Add visual branding to invoices (company/freelancer logo, tax ID, invoice number format).

Day 7 — Deploy, monitor, and demo

Deploy frontend to Vercel and enable SSL. Push database migrations to Supabase.
Set up Sentry alerts, Realtime analytics on key events (created bills, payments completed), and a simple admin dashboard (Airtable + Supabase view) for reconciliations.
Demo to a small group and collect immediate feedback for iteration planning.

Payment & invoicing workflow (how money flows)

The simplest production-ready flow used in the prototype:

Organizer creates bill + items; chooses split method.
App generates per-person invoice lines and a group invoice summary.
App creates Stripe PaymentIntents for each payer or a multi-pay link that accepts partial payments.
Payers receive secure links via email/SMS and complete payments; Stripe webhooks notify the app on success.
App marks line items/participants as paid, issues receipts, and updates the master invoice ledger for accounting exports.

Handling partial payments, tips, and refunds

Partial payments are tracked as line-item balances. The app recalculates outstanding totals and sends reminders.
Tips are captured as optional line items and allocated per payer if desired or left as a group tip handled by the organizer.
Refunds are issued through Stripe with a reference back to the original invoice and a note for bookkeeping.

Tax, compliance, and audit-ready records

Even for a micro-app, invoices must be audit-ready. Implement these early:

Sequential invoice numbering: deterministic invoice numbers with date and sequence for audit trails.
Stored receipts: PDFs and raw payment confirmations stored in cloud storage with immutable links.
Export capabilities: CSV/QuickBooks Online export for tax prep and bookkeeping (most freelancers need this).
Privacy & compliance: minimal personal data; use secure tokens for share links and encrypt sensitive fields at rest.

UX and invoice design tips that improve payment speed

Small design decisions materially affect conversion. Prioritize these for faster payment completion:

Clear CTA: “Pay $24.50 — Secure payment” beats generic buttons.
One-click payment where possible: Use saved payment methods or Stripe Link to reduce friction.
Contextual receipts: Show the event name, date, and itemized breakdown—people pay faster when they trust the charge.
Deadline and reminders: A small note like “Due in 5 days” plus automated reminders improves completion rates.

Cost and monetization considerations

Building a micro-app is cheap but not free. Anticipate these recurring costs and monetization paths:

Platform fees: Supabase (~$0–$25/mo for prototypes), Vercel (hobby plan), Stripe fees per transaction.
Messaging: Twilio/SendGrid costs for notifications as volume grows.
Monetization options: small convenience fee per transaction, paid pro features (recurring groups, branded invoices), or subscription for heavy users. For monetization patterns and creator economics see microgrants and monetization playbooks.

Metrics to track (and expected impact for freelancers)

Focus on metrics that measure cash flow improvements and time savings:

Time to payment: median hours from invoice sent to payment received.
Payment completion rate: percent of invited participants who pay without chasing.
Reconciliation time: average time per invoice to reconcile accounts.
DSO impact: measure change in days sales outstanding after adopting the app—small businesses often see reductions of several days when switching to instant pay links.

Lessons learned — practical takeaways for freelancers

Building fast teaches brutal lessons. Here are the distilled ones you can apply immediately.

Scope ruthlessly: the 7-day constraint forces prioritization. If a feature isn’t core to payment completion, defer it.
Use managed services: outsourcing auth, payments, and storage reduces security and compliance burden.
Automate reconciliation: wire webhook-based reconciliation early; manual matching kills time and confidence (see automation patterns at prompt chains).
Design for trust: invoices should look professional and include clear receipts and organizer contact info—this reduces disputes.
Iterate with real users: test with small friend groups or existing clients; watch them click and ask why.
Build exports: accountants and taxes demand CSV/PDF exports—add this before going live.
Protect data: use tokenized share links and limit personal data stored in the DB.

“Once vibe-coding apps emerged, I started hearing about people with no tech backgrounds successfully building their own apps,” — Rebecca Yu (ref: TechCrunch/Substack)

Future predictions for 2026+ (what freelancers should watch)

The micro-app trend won’t slow. Expect these developments to affect how you build and monetize group-invoicing tools:

LLM Agents: autonomous agents will automate reconciliation, draft invoices, and run customer follow-ups with minimal oversight.
Embedded settlement: more payment processors will offer instant settlement and programmable payouts, making split payments seamless.
Standardized e-invoicing: global e-invoicing standards and ISO 20022 adoption will reduce cross-border friction for small businesses.
Identity-first flows: WebAuthn and decentralized identity schemes will simplify secure payer verification without heavy onboarding.

A 7-day checklist you can reuse

Day 0: Define MVP plus acceptance criteria and wireframes.
Day 1: Setup DB + Auth (Supabase/Clerk).
Day 2: Build bill creation and split algorithm.
Day 3: Implement group invoice generation and secure share links.
Day 4: Integrate Stripe and webhooks for reconciliation.
Day 5: Add receipts, partial payments, and refund flows.
Day 6: UX polish and user testing.
Day 7: Deploy, monitor, demo, and capture feedback.

Final thoughts

Building a dining app to split bills and send group invoices in seven days is achievable—and instructive. The exercise forces you to prioritize payments, trust, and automation. For freelancers, the biggest wins are:

Less time chasing money
Faster reconciliation
Professional invoices that reduce disputes

Use modern managed services, automate reconciliation with webhooks, and design invoices for clarity. That combination delivers faster payments and better cash flow—exactly what small businesses need in 2026.

Call to action

Ready to prototype your own bill-splitting micro-app? Download our 7-day project template and invoice design pack, or hire an expert to jumpstart your build. Start reducing DSO and getting paid faster—one group dinner at a time.

invoices

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