Pay for your cart

Pays every line (or the items given, by line id; the others stay in the cart) in one go — the same rules as POST /api/v1/orders/batch: all checked first at today’s price, none placed if any cannot go, then each placed on its own. The lines placed leave the cart; one that failed at the last moment stays, with its reason. Send an Idempotency-Key per attempt (a retry with it is that same attempt) and max_total, the total you showed. dry_run: true checks only and also returns the cart; when your balance holds only part of it, the answer’s fit names the lines it pays for now — send those as items, with max_total = fit.total, under the same key.