Xero now stays authorised so you don't have to re-authorise every 30 minutes.
If you want to export invoices to more than one account in Xero you need to change the account that you are logged in to in settings before you export your invoices.
How to change the account
1. Click on settings and select Integrations in the dropdown.
2. Click on the Edit settings button next to Xero
3. In the popup, select the account that you want to sync invoices to
4. To add a new account or organisation click + Xero Account and login to Xero
5. Select the account that you want to add and click allow access. This organisation will now appear in the connected accounts list