Hi,
You need to change the item amount in invoice to 1002 as well. The difference 3 will be allocate to the consumption account.
GR debit 999 GL account in account assignment tab
credit 999 GR/IR clearing account
IR credit 1002 account payable to vendor
credit 999 GR/IR clearing account
debit 3 GL account in account assignment tab
Best regards,
Polly