It depends on your settings in Supplier Automation. When you export the documents to Xero as 'Bills (Invoices)', please check the 'Approval status' in Supplier Automation and adjust as needed. 

In case you need to export the documents as 'Bank Transactions/Expense Claims, the 'Approval status' option is not available.

Go to your Supplier Automation:

Check the Export Destination:

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