We haven't received any reports about this issue, Hannah.
Before anything else, verify that you are using the correct QuickBooks account and that VAT is enabled.
I recommend clearing your browser's cache and Intuit-specific cookies to help restore the ability to add VAT to your invoices. Cache-related issues can cause QuickBooks to load incorrectly.
To have the best experience with QuickBooks Online, you may want to consider using another supported browser. Different web browsers can have different levels of compatibility and performance.
If there's anything else you need assistance with, just let us know.
