As requested by customers, the (product or billable item) item code is now used when creating an invoice on Xero.
The image below shows a Xero invoice created by Cliniko with the Item Code filled:
On the integrations page (Settings > Integrations) we have added a table with all invoices that have been synced to Xero. We also show their status and their error message (if any). To open this table, click on the blue link "View synchonised invoices" at the bottom.