Reconciliation at scale: what we learned building Nexily Finance

Matching two clean datasets is easy. Real payment data isn't clean — processors report fees differently, refunds arrive days apart from the original charge, and currency conversion introduces rounding that varies by cents depending on when the exchange rate was captured.

We spent more engineering time on the exception-handling path than the happy path. Every unmatched transaction gets a reason code, a suggested resolution, and a one-click way to accept or escalate it — because a reconciliation tool that just flags 'this doesn't match' without saying why is barely more useful than a spreadsheet.

The result is a system finance teams trust enough to stop double-checking it by hand, which was always the actual goal.