Is a credit note sufficient?

So you're not going to submit the invoice? (Or maybe you just don't have it.) And then you're going to submit the credit note?

I think that would be allowed, but I wouldn't do it. If you don't stop the original invoice in the accounts (i.e. the cost for the accounts), then I wouldn't enter the credit note (which would reduce your costs) either. Seems perfectly defensible to me, no cost for that purchase specifically in my accounts, so no negative cost either (which is what the credit note is).

I wouldn't enter a credit note either if I hadn't entered the original invoice. It seems a bit strange to me, apart from the fact that it's not 'good' for your accounts because it reduces your costs.