Enable inventory tracking
When you receive inventory from your supplier, the transfers feature updates the number of items that you currently have available in your store, which means that you don’t need to do it manually. In order for this to work, you must enable Shopify’s inventory tracking option for your products and variants.
To enable inventory tracking:
From your Shopify admin, go to Products.
Click one of your products.
For a variant, click Edit next to the variant in the Variants section:
In the Inventory section, click the Inventory policy drop-down list and select the option Shopify tracks this product's inventory:
After you enable inventory tracking, you can create a transfer.