Quantity restriction refers to a limit on how many gift items a shopper can add per instance (i.e., minimum, maximum qty).
It also helps merchants to automatically "pre-pick or pre-select" a gift item on behalf of the shopper by setting the minimum value from "0" to e.g., "1". In this way, shoppers won't miss any gift promotions, and it reduces their interaction with the widget, allowing them to focus more on shopping in your store.
Minimum = 0
Maximum = 1