With Xero invoices, product fields such as weight, commodity information and size are not supported. However, you are still able to set up Shiptheory so that your products still have the necessary information if required. There are a few different ways to do this.
Use the default weight field-
In the Xero settings in Shiptheory, you are able to set a default weight for all products from Xero without weight, you can see the option for this in the "General Settings" for Xero:
Update your products manually in Shiptheory-
All of the products that are brought in from Xero will be saved into your Shiptheory products page. If you navigate to this page you are able to edit the information that Shiptheory has for these products and once saved, Shiptheory will use this new information for each subsequent time that product is used. You can see some more information on this in this guide: http://support.shiptheory.com/support/solutions/articles/24000038188-updating-product-data
Use the product data from another channel-
If you are using other channels alongside Xero that import this product data when sending through orders, the orders from Xero will use the same product data when applicable. As long as the SKUs for the products are the same, and the product has been sent through Shiptheory by this other channel before, Shiptheory will use that same product information to fill in the blanks brought through from Xero.
If you have issues or questions about any of these methods, please don't hesitate to contact support.