Hi @Hannah_Rees
@BFSLtd is partly right but there are quite a few ifs, buts & maybes to add. To avoid confusion, a couple of questions...
First point is, are you VAT registered?
(I'm also assuming you're in the UK)
Second, is the invoice for goods (physically imported into the UK), goods (remaining outside the UK) or services (delivered/consumed if that's the correct phrase inside or outside the UK)?