Let me share the possible reasons why the system didn't recognise Dorset when setting up tax within QuickBooks Online.
First, let's make sure that we've signed up QuickBooks account to the correct region. Otherwise, QuickBooks won't allow us to use another country for the tax setup. However, if we are sure that we're using a QuickBooks account based on our country, the process should normally allow us to set up tax without getting an error message.
We can try to refresh your browser by pressing F5 on your keyboard or clicking the Reload icon. You can also try accessing an incognito window to better isolate this matter. Here's how to log in a private browser:
Google Chrome: Ctrl + Shift + N
Microsoft Edge: Ctrl + Shift + P
Firefox: Ctrl + Shift + P
Safari: Command + Shift + N
If we're able to set up tax, let's go back to our main browser and clear the cache. It may have too much historical data from previously visited websites, which causes this kind of unusual behavior. It makes QuickBooks work efficiently and avoid experiencing odd behavior. Also, we can use other supported browsers in QBO since each of them uses a different cache storage folder on your computer.
Here are some articles that provide additional information about the tax setup in QBO: