It's tricky with Simple Delivery. The buyer has to buy the items all at the same time and put each one in their basket (on a PC, not the app). Then they will be automatically combined.
If they dont use the basket the items won't not be combined but you can just send them together anyway although some will be untracked. Or you can cancel/refund the transactions with the buyer's agreement and relist with items on one listing and a single postage cost for the buyer to buy and pay again.
