When an invoice is generated in Re-Leased, upon sync with Xero, it will pick up the Xero invoice branding and (depending on your settings) the Xero invoice number.
Automatically generated rent invoices set to be emailed are sent after this sync takes place. This means your tenant is receiving the Xero invoice, the same as if you had sent it from Xero.
The appearance of the invoice is set up in Xero's settings menu, under Invoice Settings.
Multiple branding themes can be set up in this area. Within Xero, each contact can be edited to apply a specific branding theme. If no branding is selected, the first branding theme in your list is the default.