Hello there, SPARES4REPAIR.
I’m glad to know you’re acclimated to the tasks you can do in QuickBooks Online (QBO). Let me help and guide you on how to move past the error in your VAT return.
The messages you encountered indicate that the items are set to no VAT instead of inclusive or exclusive of VAT. To sort out the issue, click the Review Now button to show the affected entries.
You’ll have to open the transaction one at a time. Then update the tax code on the transaction’s page to fix it.

Here’s an article that provides more insights into this process: Introduction to QuickBooks VAT error checker. It contains solutions on how to resolve each VAT-related issue.
Additionally, these resources will guide you on how to keep accurate records of the tax that you collect and pay. From there, you’ll learn about submitting a tax return and other VAT related-activities.
Keep in touch if you have any clarifications or other tax concerns. I’m always glad to answer them for you. Wishing you and your business continued success.