I can not see vat field while inputting supplier invoice

Thanks for visiting our forum and letting us know about your VAT concern, @diraj-hiwayhifi-,

The VAT field on bills is default when your QuickBooks Online account is enabled for VAT filing to HMRC. If you're unable to see this option, given that the tax feature is already set up, try signing in to a private window and see if it works there.

Use any of the following shortcuts to launch a private browser:

Google Chrome: press Ctrl + Shift + N  
Mozilla Firefox: press Ctrl + Shift + P
Safari: press Command + Shift + N

Once done, process the supplier's invoice through the + New icon then Bill. You will see the VAT column beside the Amount. See this:

If you're still unable to see it, let's go back and check your VAT setup in the Accounts and Settings page. Here's how:

1. Click the Gear icon and select Accounts and Settings.
2. In the Advanced menu, click Accounting.
3. Double-check if the Default tax rate selection drop-down shows No VAT.
4. If it does, change it to Exclusive of Tax or Inclusive of Tax.
5. Hit Save and then Done.
   

Check out this VAT Resource page to learn more about handling customer and supplier taxes in QBO: VAT for QuickBooks Online UK

If you have any other questions or need further assistance with this topic, let me know in the comment below. I'll be more than happy to help you anytime.