Hi FaRis,
Yes, you do this on ebay, not Auctiva. If you have a store, it will be in your selling manager page in the "Awaiting Payment" section. If not, it will be in your summary page. You'll need to find the items awaiting payment under your "sold" heading. I'm trying to remember if you have record #'s if you don't have a store. If you do, click on the record #. This is the number ebay assigns each sold item. This will bring you to the transaction page where you can adjust the total as I said in my previous post. If you don't have record #'s, you might be able to adjust the total when you click on "send invoice."
If this doesn't work, there are still a couple of ways to adjust the total. I'll be here for 2-1/2 more hours - except 1/2 hour walking the dog
.