Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Four | Buy Now, Pay Later
FOUR MAKES ONLINE SHOPPING SIMPLE, FLEXIBLE, AND REWARDING.
Free · In-app purchases
PRICE
Free
In-app purchases
BUSINESS MODEL
Freemium
No overall Grossing estimate available
RATING
★ 4.8
119,224 ratings · Top 5%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included19 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Four | Buy Now, Pay Later: map the core Shopping workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Include more diverse payment methods like Apple Pay and Google Pay.
Assumption to check: Limited payment options for users
Validate with people who use this workflow before building.
Hypothesis 2
Simplify UI design for a cleaner browsing experience.
Assumption to check: User interface can be cluttered
Validate with people who use this workflow before building.
Hypothesis 3
Implement a faster in-app support chat feature.
Assumption to check: Slow customer support response times
Validate with people who use this workflow before building.
Hypothesis 4
Integrate a recommendation engine based on user behavior.
Assumption to check: Lack of personalized recommendations
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
FOUR MAKES ONLINE SHOPPING SIMPLE, FLEXIBLE, AND REWARDING. Buy now, pay later at hundreds of online retailers. Split your purchase into 4 easy payments—paid every two weeks—so you can shop what you love while staying on budget. Manage every order in one shopping app and enjoy a faster, smoother checkout experience. Upgrade to Four+ for access to exclusive stores, special offers, and more ways to shop online. WHY SHOP WITH FOUR? • PAY IN 4 INSTALLMENTS Split payments over time with clear schedules so you know exactly what’s due and when. • FLEXIBLE PAYMENT PLANS Stay on budget with predictable due dates and helpful payment reminders. • ONE SHOPPING APP FOR EVERYTHING Browse partner stores, track orders, and manage your payment methods in one place. HOW FOUR WORKS 1. DOWNLOAD the Four shopping app and sign up in minutes. 2. SHOP ONLINE at your favorite Four partner retailers. 3. TAP “PAY WITH FOUR” at the bottom of your screen when you’re ready to check out. 4. PAY EVERY TWO WEEKS — your first payment today, the rest in 2-week intervals. WHY USERS CHOOSE FOUR • Quick and easy sign-up process • Access to hundreds of online shopping options • Manage your installment plans and track spending • Get notified before each payment is due • Works with top online retailers for a seamless checkout DOWNLOAD FOUR TODAY and discover a better way to shop online—buy now, pay later in 4 installments, and stay in control of your spending. Users must be 18 or older, a U.S. resident, and meet additional eligibility requirements. Not available in NM. By using the Four app, you agree to Four’s User Agreement and Privacy Policy. https://www.paywithfour.com/legal/user-agreement https://www.paywithfour.com/legal/privacy-policy
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Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
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Expo
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Zustand
React Native Reanimated
BUILD KIT DIFFICULTY
Expert
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
