One in-flight purchase: the items, the buyer, the price and the payment, with a status that says what's needed next.

Required at the top level: id, line_items, status, currency, totals and links.

What is being bought: an item, a quantity and the store's price. Quantities can be in units, weights or volumes.

The store's answer is authoritative, including the unit it sells in.

Who is buying: name and contact details.

Identity linking, where a store supports it, lets the buyer use their store account.

Delivery or pickup, the destination and the option chosen.

An extension to checkout, declared by nearly every verified store.

What the purchase costs: subtotal, delivery, tax, discounts, and one total they add up to.

A platform may check that the parts add up to the total, and must not complete on its own if they don't.

The payment instrument, collected through a handler the store declares. The store never needs to handle raw card numbers.

Payment is shared with other verticals: terms, split payments and 3DS step-up.

What the store needs or wants to tell the buyer: errors, warnings and notices, each pointing at the field it concerns.

Error severity tells the platform whether it can fix the problem itself or must hand over to the buyer.

A link to finish on the store's own checkout.

Required whenever the status is requires_escalation.

The placed order's id and permalink, once completed.

Must not appear while the status is complete_in_progress.