Hi, you probably redirect it to a specific page on that site? You can't redirect to a page in the site your taking offline.
It's meant for redirect all traffic to another site or a page outside of the Kentico site.
So for instance have domain1.com
offline mode can be
- domain1.com/offline.html (another physical page file you have on disk that's not processed by the Kentico system)
- subDomain.domain1.com (different application)