If you’ve already paid for a number of items you ordered from the same seller, and the packages haven't been marked as shipped, the seller may still be able to combine shipping if you ask them.
How to combine shipping
Many sellers automatically combine shipping if you're buying multiple items from them. All you need to do is add the items you want to buy to your cart and you'll see the combined shipping total at checkout.
If the shipping section of the listing doesn't specify shipping costs for additional items, you'll need to ask the seller before you pay. If the seller agrees to ship the items in one package, they'll send you a combined invoice detailing all the items and the new cost of shipping.