How do I enter a Vat only invoice?

Creating a VAT only invoice is a breeze, @usersallyturner26.

You'll need to enter the full VAT rate upon creating your transactions to receive a 100% VAT payment. 

To do that, click on the + New icon at the left pane and select Invoice. Once done, enter the information needed on the entry and select the full rate of the VAT that you're going to use. Please see the sample screenshot attached for reference: 

I've added here some great links that you can visit about entering VAT in QuickBooks Online and on what are the common codes to be used:

• Set up and edit VAT settings, VAT codes, and VAT rates
• Common VAT Codes

Thanks for visiting the Community. Please let me know if you have any other questions. I'm here to help. Take care!