Xero has the ability to add line tracking on an invoice. To set these up you will need the tracking name from inside of Xero, for example "Product Group". You can then set these on the item itself, or using the retailer settings.

The format for the tracking categories is semi-colon delimiter (;) with multiple tracking categories separated by a pipe (|) such as

{Tracking Name};{Value}|{Tracking Name};{Value} 

On the item, fill in the ExtraInfo1 field

On the retailer settings, fill in the category

Note that the retailer settings will be populated first and therefore override the item setting if the tracking name is found in each.