A personal finance management app with Plaid bank connection and Stripe subscription billing — 14 weeks.
The client had a clear product vision and a pre-launch waitlist of 1,200 people. They needed a developer who understood Plaid's token management, Stripe's subscription lifecycle, and the security requirements for an application handling financial data. We built and launched in 14 weeks.
Building a fintech application with Plaid integration, Stripe subscription billing, and financial-grade data security with no technical cofounder
The client was a solo non-technical founder who had validated the problem (users manually tracking spending across 4 bank accounts in spreadsheets) and built a waitlist of 1,200 people. They'd tried to hire a developer through Upwork — three separate contractors over 6 months — and had nothing to show for it. The third contractor had started a Plaid integration, gotten confused by the OAuth token refresh lifecycle, and abandoned the project with $8,000 of work that didn't function.
The financial data complexity that tripped up the contractors: Plaid's Item and Access Token model (a single Plaid Item represents one bank connection; Access Tokens expire and require refresh through the Plaid Link update flow); the requirement to handle Plaid webhook events for real-time balance and transaction updates; and the security requirement to encrypt Access Tokens at rest (storing a Plaid Access Token in plain text is a security vulnerability — it allows anyone with database access to query any user's bank account).
A production fintech web application launched to 1,200 waitlist customers with Plaid bank account connection, transaction categorization, and Stripe monthly billing
Stack: Next.js 14, Convex (database + real-time), Clerk (auth), Plaid (bank data), Stripe Billing (subscriptions), Resend (email), Vercel.
Plaid integration: Plaid Link embedded in the onboarding flow. Access Tokens encrypted at rest using AES-256 before storing in Convex. Plaid webhook handler for item updates, transaction sync, and error events. Token refresh via the Plaid update mode Link flow, triggered on webhook ITEM_LOGIN_REQUIRED events. Transaction sync with category mapping.
Transaction processing: Transaction categorization using Plaid's built-in categories with a custom override layer for the client's category taxonomy. Running balance calculation per account. Monthly spend-by-category aggregation for the dashboard.
Stripe billing: Free tier (1 bank account) and paid tier (unlimited accounts, unlimited history). Stripe Billing for subscription management with Stripe Customer Portal for self-serve management. Webhook handling for subscription status changes with feature gate updates.
Security: All financial data in Convex with row-level access control enforcing user data isolation. No financial data in client-side state beyond what's needed for the current view. Audit logging on all data access.
One honest number to start.
Fixed-scope, fixed-price. The number below is the starting point — final scope is built from your brief.
A production fintech web application launched to 1,200 waitlist customers with Plaid bank account connection, transaction categorization, and Stripe monthly billing
Three steps, every time.
The same repeatable engagement on every project. No surprises, no mystery, no billable ambiguity.
Brief & discovery.
We send you questions, then get on a call. Output: a written scope with every step, feature, and integration listed.
Build & ship.
Fixed schedule, weekly reviews. No scope creep unless you change the scope — and if you do, we reprice it transparently.
Warranty & retainer.
30-day warranty on every launch. Most clients stay on a monthly retainer for ongoing features and maintenance.
Results
- 1,200 waitlist customers onboarded in the first 2 weeks
- 340 converted to paid plans in the first month (28% conversion)
- Zero Plaid integration errors in the first 90 days
Related engagements.
Questions, answered.
Each bank connection is a separate Plaid Item with its own Access Token and webhook subscription. The frontend flow allows users to connect multiple institutions through the same Plaid Link flow.
Plaid sends a webhook event when a user's bank connection requires re-authentication. The application responds by marking the connection as requiring update and sending the user an email with a link to re-authenticate through the Plaid Link update mode.
Financial data applications with Plaid and Stripe: from $35k. Fixed-price.
Tell Ryel about your project.
Describe what you’re building and what outcome you need. You’ll have a written, fixed-price scope within the week.