External invoices now inherit their order's currency

POST /api/v2/orders/:order_id/invoices used to stamp every external invoice as USD, even when the parent order and its workspace were in another currency. A EUR workspace recording its external sales would see EUR on the order and USD on every invoice under it. The invoice's currency now comes from its parent order, so it matches the currency you are actually selling in.

That matters wherever the stored value is read directly: exports, reporting, accounting sync, and any integration that reads currency from the invoice and trusts it.

Agent examples: record an external sale in a non-USD workspace and read back invoices that match the order · reconcile external invoice totals against a EUR or GBP ledger without converting by hand.

Resources: Orders::Invoice · Order