The problem is: ebay doesn't allow 2 sales on the same transaction. When
you accept the offer as a seller, ebay considers it as sale 1 and
because of that combined shipping is not available, as it would be sale
2. The only way is to refund the buyer ...
you don't have to send combined invoice, just tell the buyer to pay full
basket price and then refund the shipping discount via paypal after
creating shipping label.
