You can get three different kinds of 'warnings' after you have pressed search on dokkansearch:

The first one tells you that you have to choose a region. [1] You have two options: Global or Japan. 

The second warning also has to do with a missing setting. You forgot to choose either Android or iOS as the device. [2]

The last one will only displays when you search for an account that isn't in the database. It doesn't mean that the website isn't working correctly; it just means that you have to change your search settings and try it again until it works and an account can be found.