Reduced fees and delays: caching courses and routing payments

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💡 18+. Engineering material for iGaming platforms and fintech products. Not a call to play. By "payments" we mean deposits/withdrawals through PSP/banks/crypto/ewallets.

1) Purpose: Pay faster and cheaper without losing control of risk

Speed: less than "cold" expectations (3-DS, batchy bank, network confirmation).

Cost: Minimize PSP/bank/network fees and conversion spread.

Reliability: zero-loss invariants: one debit/credit, predictable rate.

Compliance: regional rules, sledge screening, RG/AML before submission.

2) Course service (FX) with caching: how to arrange it correctly

2. 1 Sources and calibration

Price-feeds: liquidity providers/FX-API/PSP quotes/cash registers.

Normalization: single format 'pair/base/quote/scale', mid-rate + margin ('markup _ bps'), time to get 'as _ of'.

Calibration on the PSP: the PSP part returns the "effective heading" in the response; store rate cards per method/PSP/geo.

2. 2 Cache and TTL

Hot cache (Redis) for frequent pairs (EUR↔USD, EUR↔GBP, USD↔BRL, etc.).

TTL by volatility: G10 - 30-120 c, EM - 10-30 c; stables - 60-300 s (by provider).

Grace window: tolerance for using the "rotten" course of N seconds to complete intents already started.

2. 3 Slippage protection

The client is given a temporary quote with'expires _ at'and allowed drift (for example, ± 20 bps).

When executed:

if the market has left within drift → we apply the "booked" rate;
if you go further → re-quote (re-confirmation) or "best-effort" on brand policy.
For conclusions - budgeted FX: conversion spending limit, transaction rejected if exceeded.

2. 4 Idempotency and atomicity

All FX transactions have an'X-Idempotency-Key 'associated with the transaction amount/pair/type.

Ledger entry and course fixing are one saga: 'quote. lock → debit/credit → quote. release`.

Rates in monetary records are stored as minor units + scale, with no floating point.

2. 5 API (reference)

Get Quote (Cached)


GET /v1/fx/quote? base=EUR&quote=USD&side=buy&amount_minor=100000
→ 200 {
"pair":"EUR/USD","rate":"1. 08123","markup_bps":15,  "expires_at":"2025-10-23T12:00:15Z","quote_id":"q_abc"
}

Book course and write off


POST /v1/fx/execute
Headers: X-Idempotency-Key: fx_exec_001
{
"quote_id":"q_abc","amount_minor":100000,"pair":"EUR/USD"
}
→ 200 {"status":"filled","avg_rate":"1. 08125","fx_entry_id":"fx_77"}

3) Payment routing: choose the fastest and cheapest way

3. 1 Routing factors

Geo/currency/method: map/SEPA/SWIFT/ewallet/crypto.

Fees: fix +% + FX-markup, PSP/bank hidden charges.

SLA: p95 'submit→settled', success-rate, code failure.

Cut-off and settlement windows: banks (SEPA T + 0/T + 1), crypto networks (load/gas), output.

Risks: sanctions/AML/velocity-limits/chargeback-profile.

Availability: channel/PSP status, merchant limits, treasury balances.

3. 2 Cascades and bandit strategies

Deterministic rules for "hard" requirements (jurisdiction, license, amount).

Top - ε -greedy/UCB to choose between several suitable PSPs: minimize 'cost _ per _ success' and delay.

Warm-up to new channels with reduced traffic + quick stop on degradation.

3. 3 "Smart" Retrai

We repeat only retryable codes (timeouts, transient, bank offline).

Hedged-requests (rarely, carefully): parallel launch on 2 PSPs with loser cancellation - for VIP/critical amounts, if legally permissible.

Always with idempotent PSP tokens to avoid double scrapping.

3. 4 Schedule accounting

Cut-off calendar (SEPA, SWIFT, local schemes), "holidays" by country.

Scheduler: if

3. 5 Crypto routing

Network selection by 'fee _ per _ byte/throughput/ETA', white lists of addresses and travel rules (Travel Rule between VASP).

Dynamic gas: calculation maxFee/maxPriority, pause of low-priority outputs at gas spikes.

3. 6 API (reference)

Route selection


POST /v1/payments/route
{
"amount":{"minor_units":5000,"currency":"EUR"},  "method":"card","geo":"DE","direction":"payout"
}
→ 200 {
"route_id":"rt_001",  "candidates":[
{"psp":"A","eta_sec":420,"cost_minor":85,"success_rate":0. 91},   {"psp":"B","eta_sec":360,"cost_minor":120,"success_rate":0. 96}
],  "recommend":"B"
}

Execution (idempotent)


POST /v1/payments/submit
Headers: X-Idempotency-Key: pay_001
{ "route_id":"rt_001","psp":"B", "fx_quote_id":"q_abc" }
→ 202 {"payment_id":"pm_777","status":"SUBMITTED"}

4) Netting, butching and on-us optimization

On-us (within the ecosystem): settlement without external PSP → zero commission, instant SLA.

Netting: summarize small cashouts into one external transfer (banks/crypto) with detailed posting in Ledger.

Butching: SEPA files, crypto butches (UTXO consolidation/stablecoin butch) - reduce cost due to wholesale gas/commissions.

5) Cost and speed oriented telemetry and SLO

SLI/SLO:

p95 'route→submit' internal <150-300 ms, p95 'submit→settled' over the channel: cards/ewallet 5-30 min; SEPA T+0/T+1; crypto ≤ 10 min, p95 'FX quote→execute' <1 s, share of "re-quote" ≤ 2-5% (market dependent), "lost/duplicated" = 0.
Cost KPIs: 'cost _ per _ success', "spread per 1000 units," fee-burn over network/PSP, FX-PnL.
Alerts: surge re-quote, degradation of success-rate/ETA in a specific PSP/network, cost_per_success growth, increased 'IDEMPOTENCY _ MISMATCH'.

6) Observability and audit

Structured JSON logs: 'trace _ id', 'route _ id', 'payment _ id', 'psp _ ref', 'fx _ quote _ id', error codes.

OpenTelemetry: spans'route. select → fx. quote → wallet. debit → psp. submit → webhook. settled`.

WORM audit: changes in FX margin, routing rules, priorities, cut-off calendar.

7) Treasury and balances

Reserves per channel/PSP/network, automatic rebalancing taking into account traffic forecasts.

Minimum balance policies and "no new payouts" stop mode when underfunded.

Hedge: Auto swap stables/fiat on plan to capture spread.

8) Reconciliation and reports

FX register: quote_id ↔ execute_id ↔ payment ↔ conductings of Ledger.

Daily PSP/bank/network reports ↔ Ledger: categories' match/timing/missing/amount _ mismatch '.

Separate FX-PnL report: realized spread, cost of quotations, re-quote losses.

9) Architectural blocks (microservices)

fx-service: collecting feeds, cache, slippage policies, quote/execute API.

router-service: rules, bandit logic, cut-off calendar, channel status.

treasury-service: balances, rebalance, budgets.

payments-orchestrator: sagas, idempotency, webhooks, DLQ.

Везде — outbox/CDC, partition-keys по `tenant/brand/region`.

10) Checklists

Platform/Operator

FX cache with TTL on volatility, slippage policy, quote. lock/execute.
Idempotency on 'fx. execute` и `payments. submit`.
Routing with deterministic rules + bandit over.
Cut-off calendar and network schedules; scheduler for T + 0/T + 1.
Telemetry: SLO by ETA/Success/Cost; dashboard FX-PnL.
WORM audit of margin/rule/calendar changes.
Netting/butching enabled; on-us optimization.
DR/xaoc exercises: PSP drop, spike gas, volatility jump.

Integrations/PSPs/FX Providers

Return effective rate/fee in response; stable idempotency tokens.
Signed webhooks (HMAC/EdDSA), retrays up to 2xx, dedup by 'event _ id'.
T + 1 reports for reconciliation, integrity (hash/PGP).

11) Red flags (anti-patterns)

Conversion at the "market" rate without fixing 'quote _ id' and validity period.

The lack of slippage restrictions → a negative surprise to the player.

Routing is "hard-wired" into code without telemetry and A/B.

Retrains to the same PSP codes that are not retracted (for example, hard decline).

Ignoring cut-off/calendars → systematic delays T + 1 +.

Netting/butching is disabled at high commissions.

Unsigned webhooks/validity windows → replays.

No outbox/CDC → "lost" events and discrepancies in reports.

12) Withdrawal

Reducing fees and delays is not a "magic" one switch, but a system of solutions: cached and managed courses with slip protection, smart routing with cascades and bandit logic, accounting for schedules and balances, plus netting and butching. Add idempotency, outbox/CDC, SLO telemetry and WORM auditing - and your payments start to go faster, cheaper and once, while remaining transparent to the player, finances and regulator.