I refer to my support ticket 433877, it would appear that Kashflow does not deal with EC Sales particularly well & you have to have a separate sales nominal for EC Sales - VAT registered client so the invoice is included in Box 8 plus an EC Sales List & another nominal for EC Sales - NON VAT registered customers. Currently there seems to be an inability for Kashflow to determine clients who are in the EU & include the sales in BOX then include ONLY those that are VAT registered in the EC Sales list.
I have never quite understood how you are supposed to report sales of goods under the reverse VAT rules - HMRC guidance only ask for you to list sales of services under this!