Cuando falla al contabilizar factura, tira un error al loggear.

[lukio]

                 'XmlResponse: %s\n',
                 last_invoice.id,
                 last_invoice.type, last_invoice.party.rec_name,
-                str(last_invoice.pyafipws_xml_request),
-                str(last_invoice.pyafipws_xml_response))
+                str(last_invoice.transactions[-1].pyafipws_xml_request),
+                str(last_invoice.transactions[-1].pyafipws_xml_response))

El problema es que invoice no tiene el atribute pyafipws_xml_request, sino que lo tiene el modelo de Transactiones de AFIP.