Domain Bundle · Senior
Fintech Backend Bundle
Backend depth plus the compliance, security and money-correctness questions fintech asks.
Idempotency, ledgers, PCI, KYC/AML and reconciliation, the fintech-specific angle.
- Questions
- 360
- Topics
- 20
- Pages
- 300pages
- 360 questions, every one with a model answer
- Backend pack + fintech module
- Ledger & money correctness
- Compliance & security
- Payment flows
Get the Fintech Backend Bundle — $29
One-off. Delivered as a PDF by email the moment payment clears.
Prices shown are a USD base. Your local-market price is calculated at checkout in your own currency, plus any local sales tax.
What is inside
20 chapters, in the order the interviews tend to ask them:
- Representing money correctly in a codebase
- Double-entry ledger design
- Concurrency control for financial writes
- Idempotency keys and safe retries
- The payment lifecycle as a state machine
- Webhook delivery, verification and replay
- Disputes, chargebacks and representment
- Payouts, settlement and bank movement
- Reconciliation and break detection
- PaymentIntents, confirmation and strong authentication
- Subscriptions, dunning and recurring billing
- Marketplace payouts and split payments
- Refunds, partial refunds and reversals
- Fraud signals, rules and device intelligence
- KYC, KYB, sanctions screening and monitoring
- PCI DSS scope, tokenisation and SAQ reduction
- Authentication, authorisation and segregation of duties
- PII handling, encryption, keys and residency
- Audit trails, regulatory reporting and exam readiness
- Reliability of financial systems
How the answers are built
Each chapter opens with the checklist the question is really testing. A few from this pack:
- Store every amount as an integer count of the currency's minor unit, paired with an explicit ISO 4217 currency code.
- Every posting group has legs whose signed amounts sum to zero, which is the invariant that makes a ledger auditable.
- Read committed prevents dirty reads but still lets two concurrent debits act on the same balance value.
- A client supplied key is stored with a request fingerprint and the first response, scoped per account and operation.
- Model payment status as an explicit state machine so illegal transitions are rejected at the domain boundary.
- Verify the signature against the exact raw request bytes, before any JSON parsing or key reordering.
Questions this pack covers
- Why is binary floating point unsafe for monetary amounts?
- When should you store amounts in minor units rather than decimals?
- What does the double entry invariant actually guarantee?
- Why must ledger postings be append only rather than editable?
- Why does read committed isolation still allow a lost update?
- When do you need serialisable isolation for a transfer?
- Where must an idempotency key be stored relative to the write?
- What happens when a key is reused with a different payload?
Each one is answered in full in the pack, with the reasoning written out rather than a bullet list.
About this pack
- How many questions?
- 360, spread across 20 topics, written out in full across 300 pages.
- Do the answers just list keywords?
- No. Each answer is written as prose, because that is what you have to reproduce when someone asks you the question.
- How do I get it?
- Pay once and the PDF arrives by email immediately, with a signed download link.
- Can I get it refunded?
- Yes, if it is not what you expected. See the refund policy.
