Add extras to a cart

Adds one or more extras (such as merchandise, drinks, or parking) to an existing cart in a single request. Pick each extra from the cart’s options.extras list and send its inventory item ID with one of its price option IDs and a quantity. The request is held as a unit: either every item is added and the repriced cart comes back, or nothing changes and one error is returned. When one item is at fault, the error’s param names it, for example items[1].priceOptionId; a refusal of the summed quantity (over a cap or the remaining availability) or by the venue’s system names no item.

• Only Extra inventory items can be added to an existing cart
• Each item names the occurrence it is for — the cart’s occurrence, or, for an extra with its own schedule (a guided tour, parking), the occurrence selected for it, starting within its requirements.occurrence, with a price option from that occurrence’s inventory items; items in one request may name different occurrences for that reason
• Two items naming the same extra and price option, or an item naming an extra already on the cart, merge into one line with the quantities summed; caps apply to that summed quantity