Make sure the Base URL is the same as the URL you're using.
I had the same problem with a freshly installed Confluence 6.0.4 when I tried to apply the license. I started off by using the internal Tomcat webserver on port 8090. I then installed Apache with mod_proxy and was using the confluence.example.com, but hadn't updated the Base URL.
The XSRF failure disappeared as soon as I updated the Base URL.
you could try to temporary diable XSRF Token: https://confluence.atlassian.com/bamboo/configuring-xsrf-protection-427624344.html
But usually you should be able to update license with a valid session / token. Did you try to log out and log in again?
Hope this helps.
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