It's good to see you again in Community, Isobel.
I'd be happy to share with you how VAT codes report on VAT 100 returns.
If you're using the 20.0% ECG VAT code upon purchasing, the +/- VAT at 20% will be posted to Box 2 & 4, and the +/- net purchase to Box 7&9.
To know more how VAT codes report on VAT 100 returns, you can refer to this article: Common VAT Codes.
For future reference, you may find these articles helpful:
If you have any follow up questions about your VAT 100 return, you can reach back out by clicking the Reply button. Have a good one.