Selling multiple items in one listing and postage questions

[n1ke0]

Hi.  Looking for some help, please.  I'm usually a buyer, not a seller.  I created a listing to sell 10 of the same item.  It took me a while to work out how to change the quantity but I got there.  I then had a customer purchase two of the items but the invoice added the two items but only one lot of postage.  Gah!  So I was stuck with having to send two items out and it obviously cost me more in postage.  I had assumed that the postage cost would double if two items were purchased.  I then had to quickly amend my listing back to only one available just in case someone bought 10!  It has done my head in trying to work out where I can fix the postage for selling multiple items.  Can someone point me in the right direction please?  Many thanks in advance 

Spoiler

[eol-products]

Did you add the weight to the postage section. If you add anything below 250 grams the postage will stay the same for 2 items. If you have a second account it can be useful to test the listing using the cart.

[misty_blue_treasures]

In the postage rules, you can specify how much the postage cost will be for each additional item