Hello there, katie-houghton,
I'm here to provide how sales tax is reported on your VAT returns.
The ECS VAT code will +/- VAT at 20% to box 1 and 4+/- net purchase to box 6 & 7. You can use this page: Common VAT Codes. It provides a complete list of VAT codes and rates and how they affect your returns.
I've added these handy related articles for additional information:
Should you need anything else, let me know by commenting below. Just tag my name and I'm glad to help.