Do you support the new tracked inventory feature in Xero?

1.) if you have set up items in Xero as tracked inventory items already

2.) AND you use the item code of the item in Xero as the SKU of the sold product in Magento

then Xero will automatically reduce the stock quantity inside Xero when an exported invoice from Magento gets approved in Xero.

Please note that this is a one way process - any updates to stock quantity in Xero will not filter back to Magento. If you require anything more than the above I suggest taking a look at the available inventory addons for Xero.