I am referring to a buyer who buys several items and THEN pays, not someone who buys and pays for each one in turn. eBay customer service had similar reading comprehension difficulties when I asked them about this.

Most of the time eBay puts them all one invoice for the buyer (with the postage added up) - the seller doesn't have to do anything for this to happen. It's what almost always happens in my experience as a seller and buyer. Usually of course the buyer does request an invoice so I can combine postage.

But sometimes - it's happened to me (as a seller) about four times over the past couple of weeks - eBay does not combine the items and the buyer pays in separate Paypal transactions. I haven't followed these incidents up with the buyer to see what they did differently (e.g. if they were using a mobile phone - is there a way to discover this without asking them?).