This report has reimbursable expenses and already been exported once, but a payment has been issued (and therefore cannot be modified in Xero). You cannot export again unless you reverse this payment.
The solution for this error is...
1. In Xero, navigate to this report by going to Accounts > Purchases > select the Paid tab.
2. Click into the transaction select the blue text that says Payment:
3. Click Options and then Remove and Redo to delete the payment.
4. Re-export the report. The new export will override the current report in Xero and retain the same report ID.