I recently sold a couple of items to the same buyer who paid for them seperately.  I was unable to combine postage as this was paid for using Simple Delivery.   I know I could have cancelled the sales and relisted the items together but the buyer was not prepared to entertain this option meaning I had to post the items seperately at a needless expense to the buyer.

Simple Delivery has it's advantages but this is one area where it is not working to the benefit of it's users and needs to be more flexible when it comes to combining postage.  Could you please ask the team that looks after Simple Delivery if it could make changes allowing for the use of combining postage after payment has been made.