You may see this error when Dext is able to publish the data from your document, but is unable to send the document image through Xero’s API. This is due to specific API data size limitations with Xero.
It is important to note that Xero has a restriction on the amount of data that can be sent directly through API at a time. You can find more details on this here.
As this is an error borne from Xero directly, you can resolve it by uploading the document image directly in Xero.