When the Xero integration syncs an order to Xero, Xero calculates the total tax figure applied to an order based on the 'Tax Rate' specified for each of the items in the order.

While Fieldfolio permits setting the tax rate for a catalog (which applies by default to all products in the catalog), it's important to note that there is no synchronisation of this value between Fieldfolio and Xero. For tax to be calculated correctly for orders synced to Xero, you must ensure that the catalog's tax rate matches that set for the items it consists of in Xero, and that of the default tax rates (for both taxable and non-taxable items) set in the integration's configuration.