Processing error text means that DEAR tried to send the data to QuickBooks/Xero but failed to receive a response either due to server restart or due to some unexpected error. In this case, entry is remaining as Complete with Processing to avoid exporting duplicate data to Xero/QBO. But this special error allows to CHANGE Completed state manually to Pending, allowing to re-sync the entry in case if it is not in Xero/QBO.