Find the items in your eBay Sold summary, to the right there's a dropdown menu, select the 'send payment details' option.
An invoice will appear showing the items.
Put the combined postage amount in the postage field (do not click on the reset/recalculate option as this deletes what you've just done).
Click on the preview link to make sure it looks okay, if it does, click on send.
PS If the items have been sold via eBay's Global Shipping Programme to international buyers, you cannot combine postage.
