Hi All,
I have successfully setting up preferred domain in google webmaster.
Actually if you encounter the same error with me. What you need to do are as follow:
1. Add the other URL. In my case, I have the non www thus I need to add the www into Google webmaster
2. You will need to verify the new URL, by choosing the same method to verify the previous one. The different is, after choosing the verification alternative, you do not need to do any verification in your URL. Just click ‘Verify’.
Then message for successful verification will appear ??
You can proceed to setting your prefered domain.
Detail:
https://techrena.net/preferred-domain-google-webmaster-tools/