I cannot solve this problem. No-matter how many items a customer buys, I charge only one shipping fee of £6 80. But! This only works if the items are identical. If a customer buys two different items on my website, then they are charged £6 80 twice. I want to set up paypal so that no-matter how many different items (or sizes) they buy, there is still only a total charge for shipping of £6 80.