Connecting a product to the system of record for stock, prices, invoices, and accounting — 1C, SAP, or similar — so numbers match in both places without manual entry.
When the site and the accounting system disagree about stock or price, customers are sold things that do not exist. Manual synchronisation guarantees this happens eventually.
We treat the accounting system as the source of truth, synchronise through queues rather than direct calls, and make mismatches visible in a reconciliation report instead of silently overwriting.