Enable inventory tracking
When you receive inventory from your supplier, Shopify updates the number of items that you have available in your store, which means that you don’t need to update it manually. For this to work, you must enable Shopify’s inventory tracking option for your products and variants.
From your Shopify admin, go to Products.
Click one of your products.
Optional: Open a variant.
In the Inventory section, select Shopify tracks this product's quantity from the Inventory policy list.
After you enable inventory tracking, you can create a transfer.