DEAR cannot send overpayments over to Xero. All overpayments must be handled in Xero, since DEAR will download payments made against invoices from Xero, but not overpayments.
To solve the sync issue in case of an overpayment:
- Undo the payment in Xero.
- In DEAR, do not apply payment. Sync to Xero with no payment against the invoice.
- In Xero, record the payment of the invoice, including the overpayment.