Invoicing to Southern Ireland but delivering for them to Northern Ireland - VAT ?

We have a client who has placed an order with us who is based in Southern Ireland but wanted us to ship the goods to their sister company in Northern Ireland. Although we have invoiced Southern Ireland (which is correct) they are telling us that we need to be charging them VAT. Is that correct in this case as the company we have invoiced is based in the EU

Hi Martinr6899,

If you are sending the goods within Northern Ireland then this will be a UK supply and so there would need to be VAT 20%.
The invoice is essentially irrelevant here as the deemed Place of supply of the goods is the UK and so UK VAT applies.

Thank you.