To reach these settings, you will first need to access the Xero advanced settings in Shiptheory. First, scroll to the bottom of your Xero settings and click "Advanced Settings in the bottom left:

After that, you will be able to see the three different status update settings:

The first option there is for Shiptheory to update invoices in Xero to the status of "Order Complete" once the order has been booked in through Shiptheory and there are no un-allocated items in the parent order.

The second option is in a similar thread, that being that Shiptheory will update your invoice in Xero to the status of "Shipment Failed" if the order in Shiptheory has some sort of issue when trying to book in.

The third option will allow Shiptheory to pick up the "Notes" section of an invoice in Xero, to fill in the "Delivery Instructions" field in Shiptheory, you can use the string "instructions = x", with "x" being the delivery instructions you want to include. To send through a box count, you can use the string "boxes = y", with "y" being a value you insert. You can see the notes field here:

If you run into any issues, or have any questions at all, don't hesitate to contact support.