In version 27.1 the new Brexit postponed VAT codes add the notional VAT to the net amount when a PI or PO is created.
IF you are just posting a purchase invoice that is ok as Sage then creates a credit to cancel out the VAT amount on the supplier account.
~We use Purchase orders which are not posted until the goods arrive. The new Postponed VAT codes now result in the PO having an incorrect total for the duration until the goods arrive and the PO is updated to an invoice. This needs to be fixed as we can no longer check the balance due to the supplier by looking at the POs and there is a danger of the supplier being overpaid.