OpenSylo

I was brought in to work on the API layer, building reusable logic both apps could share instead of owning either frontend outright. Stack was Next.js with TanStack Query and Zustand hooking it all together.

On Lender I built an infinite-scrolling loan request feed with URL-driven filters, a make-offer flow with fee validation, withdrawals protected against double-debits, and optimistic wallet balance updates that roll back automatically if something fails.

Merchant had a multi-stage KYC flow with document upload, sales-platform integration for revenue checks, and a direct-debit mandate setup driven by a state machine. Shared auth, storage, and UI packages with the Lender side.

The real meat was the shared layer underneath both: idempotency patterns, optimistic updates, virtualized tables and feeds, all built once and reused across two very different flows.