How do i enable purchase to add vat rates on purchase under the tax agency ?

A pleasant day to you, @knowcross.

Adding a VAT on your purchases can be done in just a few clicks. I got you covered on how to do this.

To start with, know that if you're VAT has not yet set up, you'll need to do it first. Just go to Taxes and select on VAT, then follow the on-screen wizard.

Once done, you can now add VAT on purchases. Please follow these steps below:

1. Click on Taxes at the left pane.
2. Press on VAT.
3. Select the Edit VAT ▼ drop-down arrow, then hit on Edit rates.
4. If VAT for Purchases has not already been added, select Add tax rate.
5. Select the Purchases checkbox.
6. Give the new tax rate a name, description, and percentage rate (usually the standard), then choose an account and determine which return line you want the tax amount to appear on.

For complete details about this set up you can visit this link: Set up and record purchase taxes.

You may also consider checking these resources below to learn more about VAT rates and codes in QBO together with submitting a return: 

• Set up and edit VAT settings, VAT codes, and VAT rates
• Submit a VAT return in QuickBooks Online

Know that you can always find me here if there's anything else that you need. I'd be happy to help. Take care and stay safe!