If you have an invoice that fails to sync from Dynamics 365 to Xero, the first step is to check the Sync History records against that invoice to find the reason why the invoice was rejected by Xero.

Once you have solved the issues you can try to resend the invoice by going to the Xero details records on your invoice in Dynamics 365.

Open the record then change the export status from Failed to No and save the record. The invoice will now be reconsidered for processing the next time when Connectorly runs.