Amazon Product Advertising API Developer's Manual page 143

Product Advertising API Developer Guide
Shopping Cart Concepts
Out of Stock Items
Most items for sale are available immediately. There are times, however, when that is not true. Items can
go out of stock or very popular items, such as a new Harry Potter book, are pre-sold, that is, the book is
sold before the book is even published.
When a customer adds an item to their cart that is not available, it is added to the SavedForLater area.
Also, if an item in the cart, for some reason, becomes unavailable, Amazon automatically moves the item
in the cart to the SavedForLater items section.
It is also possible for a customer to add an item directly to the SavedForLater items area in their cart so
that they can easily purchase the item at a later date.
When items become available, you can use the CartModify operation with the Action parameter to
move items from the SaveForLater section of the cart to the Active section, which is fully described in
Moving Adding Items as Saved For Later (p. 143). Or, if Amazon automatically moved an item in the Active
area to the SaveForLater area because the item went out of stock, Amazon will move it back into the
Active area automatically when it becomes available.
Items With Limited Quantities
Many products have a limit on the quantity that can be added to a cart. Sometimes this is inherent to the
product, for example, one-of-a-kind jewelry items. Sometimes it is a limit set by the vendor, for example,
they might set a limit for big ticket items of one per customer. If you add an item to the cart with a quantity
that exceeds the maximum, CartAdd or CartCreate automatically resets the quantity to the maximum.
No error is generated. Therefore, you must verify the quantity of items in the cart with the number ordered
to determine if the quantity has been capped. If so, you must notify the customer.
Variation Parents
Variation parent items cannot be added to a cart. For example, you cannot add Apparel to a cart because
it is not clear what apparel you really want to buy. You could add one of its children, however, such as a
red shirt, size large. If you try to add a parent item, you get an error message similar to the following.
The item you specified, [ASIN], is not eligible to be added to the cart. Check
the item's availability to make sure it is available.
Variation parents do not have corresponding OfferListingId's.
Collection Parents
Collection parent items are abstractions of the items in the collection. The collection parent cannot be
added to a cart. The Collection parent is used as a name holder for the collection. Collection parents do
not have corresponding OfferListingId's.
Offers and Identifiers
ASINs identify items, such as a Harry Potter book. ASINs do not, however, identify sales information
related to those items.
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