Buy online, pick up in store
Route each online order to the nearest store with the item in stock, and hand the order off in store, at the curb, or at a locker. The store works a pick queue, and the customer gets a notice when the order is ready.
Routed to the nearest store holding the item. If the shelf count is wrong, the order moves to the next store that has it.
How a pickup order gets to the customer
Check the stock, route the order to the store, pick and stage the order, and tell the customer the order is ready.