FinTech apps fail in production for reasons the design file never showed: a retried payment that charged twice, a KYC document in a public bucket, an admin screen that could change a limit with no second person, a log line that contained a full card number. This checklist is what Codex Thrill walks through before building on the NeoBank, Lend, Pay or DocAI blueprints. It is a list of decisions, not a certification.
Name the licence and the partner first
Software does not create the right to hold deposits, lend, or move money. Write down who the licensed institution is, which KYC vendor checks identity, which issuer stands behind a card, and which scheme or acquirer settles a QR payment. If those names are “to be decided”, the architecture can still be sketched and the integration must not be pretended. The Codex blueprints are customisable starting points around those partners. They are not a bank, a lender or a payment scheme.
The same honesty applies to geography. A flow that is reasonable in one market can be the wrong control in another. Saudi e-invoicing, for example, belongs in a gateway beside a retail checkout, which is a different product from a wallet.
Draw the money boundary
Decide where a balance is allowed to change. There should be one place, with a command that has an idempotency key, an author, and a reason. The mobile app proposes. The API commits. A second tap, a timeout, or a duplicated webhook must not create a second debit. If you cannot describe that on one page, you are not ready to design the green button.
Refunds and manual adjustments are part of the same boundary. They need a second person or at least a recorded reason. An operations console without that control is how small fraud becomes a support habit.
- One service owns balance changes
- Every command has an idempotency key
- Webhooks are verified and deduplicated
- Adjustments require a reason and an author
Identity, step-up and session
Password plus a long-lived session is not a FinTech login. Decide which actions need step-up: a new beneficiary, a higher limit, a device the user has not used, a payout. Store refresh tokens so they can be revoked. Do not put access tokens in localStorage and call it done. On the server, authorise every request against the customer id. Never trust an id sent only from the client.
Staff users are a separate population. Support should see what they need to resolve a ticket and no more. Break-glass access should be noisy.
KYC documents are not user uploads
A passport photo is not a profile picture. Capture it, extract only the fields you defined, and put low-confidence or high-risk files in a review queue. Keep the original next to the extracted value so a reviewer can see a misread. Codex DocAI is a blueprint for that queue. The model does not approve the customer.
Decide retention before launch: how long the image is kept, who can open it, and how deletion works when the application is refused. Private storage, encryption and a short-lived view link are the default. A public object URL is an incident.
Logs, vendor reviews and abuse cases
Log the decision, not the secret. No full card numbers, no document images, no one-time codes. Keep an audit trail of limit changes, holds and approvals that an internal reviewer can read without a database console. Rate-limit the public steps: application start, login, OTP, payment initiate. Write down the abuse case you expect — repeated small payouts, a stolen phone, a replayed QR — and the control that catches it.
For any AI step, keep the same rule as the finance copilot: the model may propose a field or a summary, and a person accepts it when the cost of being wrong is a customer, a loan or a payment.
What to demand in the first milestone
The first milestone is not a home screen. It is a threat model on two pages, a ledger command that cannot double-post, a login with step-up on the dangerous action, a document path that is private, and an audit event you can demonstrate. After that, screens are cheap. The Codex NeoBank, Lend and Pay blueprints exist so those decisions are visible at the start of a project instead of discovered after the first real customer.
Conclusion
A secure FinTech app is a set of boundaries you can point at: who is licensed, which service moves money, which action needs a second factor, where a document lives, and what the log is allowed to contain. Build that before the visual design. The Codex blueprints are a way to start from those boundaries and adapt them. They are not a licence, and they are not a finished bank in a box.
Frequently asked questions
Does this checklist replace a penetration test or a licence application?
No. It is the engineering conversation to have before the build. Licensing, scheme rules and an independent test still apply to the institution that will operate the product.
What is the single most important payment control?
An idempotent command for anything that debits or credits, so a retry or a duplicated webhook cannot post twice.
Can AI approve KYC?
It should not. Extraction can propose fields. A person accepts, corrects or rejects, especially when confidence is low or the case is high risk.
Are the Codex FinTech products ready to white-label?
They are customisable blueprints. Each engagement adapts onboarding, ledger boundaries and partners. They are not a hosted bank.
