How the integration of payment systems works

Payments are the "aorta" of an online casino. The conversion to the first deposit, the withdrawal rate, the share of chargebacks, the support load and even the reputation of the regulator depend on how the integration with payment providers (PSP) works. Below is a practical map: what components are needed, how the request flows, where to put protection and what to count.

1) Architecture of the payment loop

Main units:

Checkout UI-Select method/currency/amount, 3DS/SCA, statuses, errors.
Gateway: routing to PSP according to the rules (country, currency, risk, cost).
Wallet (PAM/Wallet): balance sheet accounting, RG limits, 'debit/credit' transactions.
Antifraud/AML: scoring operation before and after authorization.
Webhooks (Callbacks): confirm the final statuses.
Billing/Reconciliation: daily coincidence of money in the PSP and in the wallet.
Token storage: cards/wallets via PSP tokenization, no "raw" PANs.

Routing to multiple PSPs:

Country/Bank/Currency/Limit Rules, A/B Lines, Automatic Failover on Degradation.

2) "Deposit" and "withdrawal" flows (schemes)

Deposit (card/wallet/banking):

1. 'POST/payments/init' → create an intention (amount, currency, method).

2. Redirect/SDK → 3DS/SCA/biometrics.

3. The PSP returns a preliminary status (authorized/pending/failed).

4. Webhook PSP → final status (captured/failed).

5. 'wallet/credit' by final + record RG/history limits.

Conclusion:

1. 'POST/payouts/init' → checking the vager/limits/risk.

2. Initiating payout in the PSP (ideally the same route as the deposit).

3. Webhook PSP → success/failed.

4. 'wallet/debit' on success, failure cause log, player notification.

3) Idempotence and money connectedness

Each call is with'Idempotency-Key 'and a unique' txn _ id '.

Deposits/conclusions change the balance only once - according to the final webhook.

Any repeat query returns the same'txn _ id'and status.

In conjunction with games: 'round _ id' ↔ 'debit _ txn _ id '/' credit _ txn _ id'.

4) Safety and compliance

TLS 1. 2+/1. 3, HSTS; webhooks with HMAC signature and anti-replay ('timestamp', nonce).

Tokenization of cards at PSP; PCI DSS scope reduction (hosted fields/pages).

Card SCA/3DS2, PSD2/Open Banking for Pay-by-Bank.

GDPR: PII minimization, retention, DSR processes; profile access log.

mTLS/IP allow-list for connections with PSP, segregation of the payment loop.

5) Antifraud and AML (before and after payment)

Pre-auth rules: geo/ASN, device, velocity, behavior, pass-through.

ML scoring/graph: general cards/wallets/devices, repeated chargeback.

Post-auth monitoring: cancellations, returns, quick output.

AML scenarios: thresholds, structuring, unusual routes, STR/SAR reports.

Step-up KYC: at medium/high risk before output.

6) Webhooks: reliable delivery

HMAC signature, 'timestamp' validation, and 'event _ id' deduplication.

PSP-side retreats are idempotent.

Delivery logs (success/fail), dead-letter queue and manual "replay."

Webhook does not change the balance unless the amount/identifiers match.

7) Errors and timeouts: response design

Codes: '402' (payment required), '409' (idempotent conflict), '422' (validation), '429' (rate-limit), '5xx' (incident).

Error bodies: 'error', 'message', 'trace _ id', 'details {...}' - help support and alerts.

Graceful retry on the client (exponential backoff), clear hints in UI.

8) Multiple PSP routing and failover

Quality rules: p95 authorizations, conversion, share of 3DS files, cost.

Smart router: if the metrics deteriorate, switch traffic to an alternative.

Sticky route to session/bank for 3DS stability.

Degradation plan: turning off "heavy" methods, leaving fast (P2P/Pay-by-Bank), output queue.

9) Reconciliation

Daily uploading of PSP and auto verification with wallet: matching amounts, commissions, returns.

Mismatches → cases for investigation.

Separate reports on chargeback/refund/fees, calculation of true margin by methods.

10) Metrics to keep in focus

Deposit conversion by method/bank/country/device.

Deposit/output time (p50/p95).

Share of 3DS-files, cancellations, returns, chargeback rate.

Share of manual reviews and TTV KYC.

Uptime PSP and native error-rate by route.

Cost per success and ROI by method.

11) Example of minimum API (abbreviated)

Create deposit intention

`POST /v1/payments/init`

json
{
"amount":"50. 00",  "currency":"EUR",  "method":"card",  "return_url":"https://app. example. com/checkout/return",  "idempotency_key":"b6a1-…",  "meta":{"country":"FI","device":"ios"}
}

Answer

json
{"payment_id":"pay_123","status":"pending","redirect_url":"https://psp. example/3ds/…"}

Webhook status

`POST /v1/payments/webhook` + `X-Signature: sha256=…`

json
{
"event_id":"evt_789",  "payment_id":"pay_123",  "status":"captured",  "amount":"50. 00",  "currency":"EUR",  "timestamp":"2025-10-17T09:41:00Z"
}

Enroll (within platform)

`POST /v1/wallet/credit`

json
{"payment_id":"pay_123","txn_id":"txn_555","amount":"50. 00","idempotency_key":"b6a1-…"}

12) Availability and UX checkout

Minimum steps: auto-detect countries/currencies, stored method tokens.

Local methods: bank buttons, e-wallets, Apple/Google Pay.

Transparency: commissions/ETA conclusions, operation status, understandable errors.

Accessibility: large elements, contrast, screen readers, multilingualism.

13) DR/BCP and Operations Security

Replication of payment journals, encrypted backups, quarterly DR exercises.

RPOs/RTOs are documented, flows of "deferred" payments in case of PSP failure.

WAF/bot management at the checkout, but exceptions for PSP redirects/SDKs.

14) Frequent errors

The balance changes until the final webhook → doubles/out of sync.

No'Idempotency-Key '→ A network failure retry creates a second operation.

Weak verification of the webhook signature → status substitution.

Lack of auto-verification with PSP → "quiet discrepancies."

One PSP "for everything" → downtime and loss of conversion during degradation.

Validation of 3DS/address fields "for show" → the growth of chargebacks.

15) Implementation checklist (save)

Multi-PSP router, quality rules, failover
Idempotency on each layer ('txn _ id', 'Idempotency-Key')
Webhooks: HMAC, anti-replay, delivery logs, deduplication
Tokenization/hosted fields, PCI DSS scope reduction
3DS2/SCA, PSD2/Open Banking where available
Antifraud/AML before and after payment, step-up KYC
PSP reports auto-reconciliation, non-conformance analysis
Observability: deposit/output p95, 3DS fail-rate, uptime PSP
DR plan, deferred payments, journal backups
UX tills: local methods, transparent ETA/commissions, availability

Good payment integration is not to "connect the SDK," but to build a stable contour: multi-PSP routing, strict idempotency, signed webhooks, anti-fraud/AML, auto-verification and observability. This stack increases conversion, speeds up withdrawal, reduces chargeback risks and makes the platform predictable for players, partners and regulators.