Design entities for accounts, contacts, payment methods, balances, and entitlements with immutable IDs and audit trails. Store status transitions explicitly, not as guesses computed later. Favor event timestamps over booleans. This foundation powers proration, dunning logic, and honest reporting without brittle, hidden assumptions waiting to explode.
Offer the methods your audience actually uses, then route intelligently by geography, amount, and risk. Prefer bank debits for predictability, cards for reach, wallets for convenience. Add network tokens and account updaters. Monitor acceptance by BIN and bank to adjust routing dynamically before revenue leaks become visible.
Capture consent once, prove it forever. Store mandate references, IP addresses, device fingerprints, and authorization timestamps. Use step-up authentication only when risk models require it. Make renewal language explicit and human. When disputes arise, crisp artifacts close cases quickly and preserve trust even when outcomes disagree with hopes.