Non-3D Multi-card Payment

Multi-card payments are created as separate pre-authorizations, one request for each card. Send every request to POST /payment/v1/card-payments with the same conversationId so the payments belong to one order.

All regular non-3D payment fields remain valid. For each card set paymentPhase to PRE_AUTH, paymentType to MULTI_CARD_PAYMENT, and paymentOrder to the card's sequence number. Set paidPrice to the amount charged to that card, not the full order amount.

The response uses the current CardPaymentResponse documented in the non-3D payment section. Complete the grouped pre-authorizations with the multi-card post-authorization endpoint after all card requests succeed.