Selling the same item twice is not a checkout bug. It is a stock-count bug that checkout revealed, a few seconds too late to do anything about it.
The problem
Storefronts sync inventory on a schedule. Between syncs, the shop is selling from a number it no longer has, and every additional sales channel widens the window.
Our approach
Stock is decremented by the order, not by a nightly job. The storefront, the warehouse, and the payment record read the same count at the same moment.
What it does
Storefront
Catalog, search, and a checkout that does not fight the customer.
Inventory
One stock count across every channel, moved by orders.
Payments
Capture, refunds, and reconciliation against the order record.
Fulfilment
Picking, shipping, and returns that close the loop.