Records a (full or partial) fulfilment when you ship the goods. Requires scope orders:write.

shippedAmount is optional: omit it to fulfil everything still outstanding, or send a positive
figure to fulfil part of the order. Sending 0 is rejected with 400 INVALID_SHIPPED_AMOUNT — it
used to fulfil the whole order, which is the opposite of what a merchant reporting "nothing shipped
yet" intends. Negative amounts and amounts above the outstanding balance are rejected too.

Example request:

{ "shippedAmount": 1200.00, "shippingCompany": "Aramex", "trackingNumber": "ARX123", "trackingUrl": "https://..." }

If shippedAmount is 0, the remaining unfulfilled amount is used. Partial fulfilments move
the order to PartiallyFulfilled; fulfilling the full amount moves it to FullyFulfilled.

Errors: 400 INVALID_STATUS if the order can't be fulfilled in its current state,
404 NOT_FOUND if the order doesn't exist or isn't yours.