Currently, the Payment tab isn't available in QuickBooks Online (QBO) for the UK version. However, you can connect your PayPal account to QBO. This way, your customer can pay their invoice online. Let me show you how to do it.
In your QBO account:
Go to the Apps menu.
Select the Find Apps tab.
Type in PayPal from the search bar.
Select the app and click Get App Now.
You can also check our QuickBooks & PayPal page to learn more about how PayPal works in QBO.