Yes, the idea of 30 days after invoice as opposed to after statement is problematic, but I have found a way to make that work in the traditional way.

But this is a real silly error and applies no matter how you configure the terms; if there is discount in those terms, the VAT will be wrong.

When you consider how difficult it is dealing with an SD14 return as it is, this is really going to be challenging.

As a matter of interest it does the same thing with bills, but it is immediately detected because the entry is out of balance. With sales on the other hand, you don't start by entering the total sale value; you rely on the system and hence it can go undetected.