SUMIF Problem

I’m trying to use excel to keep an accurate count of inventory for our small church bookstore (non-profit). I decided to use UPC codes on my spreadsheet so that when I scan an item that is being sold the Product name, selling price would automatically populate my spread sheet from a VLOOKUP table. It took some work but that seems to be working.

Now I’m trying to have the worksheet automatically up-date our current stock amounts when an item is sold or we buy new/additional items for the bookstore. I’ve set up a separate tab called IN-OUT Inventory where I record the quantity of items sold or added to the inventory. When I scan a UPC code and it pulls over the Product name and selling price and I enter either a negative number for a sale or a positive number for addition to inventory.

My main tab is called Current Inventory Sheet and I’ve placed a column at the end of that spreadsheet called Beg. Stock to represent the stock we are starting out with for this year. In the Current Bookstore Inventory tab the “Total Stock” column I need it to add in the beginning stock and then search for the UPC code on the In-Out Inventory sheet. If there is a match then add or subtract that number to reflect the current stock.

I thought I had this working with a SUMIF coding but it appears that it won’t add or subtract additional transactions when there is a UPC code recorded more than one time on the IN-OUT sheet. So if I start out with 5 widgets and sell 2 it records total stock as 3; however, if I then receive 20 widgets and/or even sell 2 more it doesn’t recognize that transaction.

Any help anyone could provide is greatly appreciated. Thank you!

Here’s the link to the document:

https://1drv.ms/x/c/8fc8e0832ff0a880/EeW-INANifhPuJTiQlWVCt0BEmpuYERcvgBDBK-3R9OFXg?e=TmmWtX