I can’t add tax it says to change county but this is correct ?

Welcome to the Community forum, @richard-ppprotec.

To validate your address, I suggest visiting this link: https://www.postoffice.co.uk/postcode-finder. 

Once verified, try performing some basic troubleshooting and enter the correct address again. You can use a private browser to verify if this is caused by the system or your browser. 

You can use the keyboard shortcuts below:

• Chrome: Ctrl+Shift+N
• Firefox: Ctrl+Shift+
• Safari: Command+Shift+N

Then, check to see if it works. If they are, then your main browser may have too much historical data from previously visited websites which slows down internal processes and causes this kind of behavior.

To ensure this doesn't happen again, it's a good idea to clear the cache of the browser you're using. The following article contains additional insight, as well as steps for the supported browsers: Clear cache and cookies to fix issues when using QuickBooks Online.

Please let me know how it goes. I'll be looking forward to hearing back from you. Have a great day!