How do I overide the input VAT amount in QB online for a bank payment to a supplier where payment for goods includes different VAT rates eg 20% and Zero rated goods?

I'm here to help you record your transactions, @wdmaccountancy.

When you record this as an expense, you can always add another line to add another VAT code.

Let me show you how:

1. Go to the + New button and select Expense or Bank Deposit.
2. Enter the transaction details.
3. Click the Add lines button. It is located below the last line item.
4. Select Save and close. 

You can check this article for more information on how to enter and manage expenses in QuickBooks Online and on how to record and make bank deposits in QuickBooks Online. 

To help you review and out your bank and credit card transactions and put them in the correct accounts, check this article: Categorise and match online bank transactions in QuickBooks Online.

I'm always here if you have any other concerns in recording your transactions in QuickBooks. Take care and have a great rest of the day!