Hi cjt2,
You can easily enter a transaction for 100% VAT by following the steps outlined below:
1) Click on the + sign and select Bill
2) Enter the bill details (date, payment account) and set the VAT 'Amounts are' to 'Exclusive of VAT'
3) On the first transaction line, choose the account you want to use. For the rate, enter £0.01, and for the VAT code, select the 20% Standard code.
4) On the second line, select the same account. For the rate, enter -£0.01, and choose the Exempt VAT code.
5) Scroll to the subtotal - the total of the invoice will be 0. You can then edit the amount in the VAT box to input the amount you need - this will post to box 4 of the return.
Thanks