Restrict splitting to tested payments

Select only payment methods whose complete lifecycle supports several Magento orders from one checkout. Invoice and purchase-order methods are common candidates, but compatibility depends on the actual integration.

For every allowed method, test order placement, external reference creation, authorisation or capture, cancellation, invoicing, credit memos and refunds. Choose Create Single Order for a graceful fallback, or Block Checkout when silently changing the order structure would be misleading.