Enable inventory tracking
When you receive inventory from your supplier, the transfers feature automatically updates the number of items 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.
The transfers feature will only work for those products and variants whose inventory is being tracked by Shopify.
To enable inventory tracking:
From your Shopify admin, go to Products.
Click on one of your existing products.
Click Edit next to the product (in the Variants section):
In the Inventory section, click the Inventory policy drop-down menu and select the option Shopify tracks this product's inventory:
Now that you’ve enabled inventory tracking, you can create a transfer.