does anyone know how to fix the linking and posting transactions - it keeps coming up with please select vat

Hello there, Jord. Since you are always prompted to select a VAT when it shouldn't be, it will be a good idea to reach out to our QuickBooks Live Support Team for further assistance with this unusual behavior.

To reach out to them, click the Help button in the top-right corner of your QuickBooks Online screen. Then, click on the Assistant tab and type Contact Us to view your support options. You can choose how you want to get help, whether it’s through Chat or a Callback.

For their available hours, you can read this article: Get help with QuickBooks products and services. Don't forget to select QuickBooks Online as your product.

You can always comment below if you need further assistance in posting transactions in QuickBooks Online.