Hi @MBenji,
Welcome to the Seller Community!
The COGS functionality uses a First-In-First-Out (FIFO) methodology for determining what cost is applied to the sale. This accounts for changes in the purchase price from your vendor. If you purchase 5 units of an item for $20 and then purchase an additional 10 units at $22, the first five units sold will have a COGS of $20 and then the remaining sales will use the $22 cost. The COGS is based on the Unit Cost that was used when receiving inventory and not the current Unit Cost displayed for the Item/Variation.
The first thing you'll want to do is review your stock transactions to confirm what Unit Cost that was used when receiving the inventory. Select the item from your Item Library and use the View stock history to confirm that the retail price was not mistakenly used when receiving the inventory.
Here's a sample of an item's Stock History with different costs.
The Small,Black variation was received on 7/2/23 for a cost of $17.75, then sold on 1/11 for the same cost. The variation was restocked and purchased from the vendor for $19.75. When the Small,Black sells again, it will use the $19.75 cost. If the sale had not happened and there were 2 Small,Black variations in inventory, the first sale would use a COGS of $17.75 and the second sale would use the $19.75.
Note: the same FIFO methodology is used when managing your stock for removing inventory (damage, theft, etc.).
