Real-Money-Ready Fantasy Sports Platform

The challenge

A money-handling product has to be exact under concurrency: stakes, payouts, voids, and re-settlements must be double-spend and double-payout proof even with overlapping cron runs and user double-clicks. Match results arrive from a third-party feed that can be late, incomplete, or retroactively corrected, so already-settled slips sometimes have to be re-graded, and a small team still needs sportsbook-grade security and operator control.

The solution

Designed and built the platform end to end on Next.js 16 and Supabase. Moved the financial logic into atomic Postgres functions (create slip, settle, force re-settle, void) with an append-only ledger that even the service role cannot mutate. Enforced defense-in-depth security across three independent layers (API auth, Postgres GRANTs, row-level security) backed by a runnable security test suite. Built an automated settlement pipeline on scheduled cron with a stale-aware distributed lock, a live sports-data adapter with retry and backoff, a risk and multiplier engine, and admin tooling writing to an append-only audit log.

Results

• Atomic Postgres settlement functions with an append-only, immutable ledger
• Defense-in-depth security: API auth plus Postgres GRANTs plus RLS, with a runnable security test suite
• Exact re-grading of already-settled slips when upstream stats change, via signed compensating entries
• Automated settlement pipeline with distributed locking to survive serverless timeouts
• Live sports-data integration with retry, backoff, and rate-limit handling
• Architected so the free-to-play to real-money switch is a contained change, not a rewrite