There are certain settings on the Formitize side, that are available to you to customize the information that is sent to your Xero Invoices, to access these settings in the Web Portal,
In the Web Portal, go to Settings cog > Accounts > Invoices > scroll down to Xero Settings > select the default settings you want > Save at the bottom of the page.
Note: If you do not have your Formitize account integrated with Xero, the settings will instead be called Accounting Package Settings.