Change xbox name is not possible?

Hi, as described in the title, I can't change my Xbox live gametag on the pc, I'm always redirected to the correct page, but if I want to change it and want to confirm it, it is gray and my changes are discarded. What am I doing wrong?

You can only change it once. If you want to change it again you either have to pay 10 euro, or your friends should all report your gamertag, then you will eventually get an email from Microsoft that you have to change it. Then it's free.

The thing is that I haven't even changed it yet

Then it should be possible without any problems