read what user above said (nintendo shutted down servers, you must use fan made servers)I have a Dsi on 1.4.5. When I make internet test, wifi icon becomes red after it says "succesful". What can I do about this?
Are you trying to connect to the official Nintendo servers? They turned them off for DS and Wii consoles in 2014. The only way to play over wi-fi is to use AltWFC or Wiimmfi.
Quick instruction of using AltWFC in first post -> https://gbatemp.net/threads/every-day-online-play.423984/
If you already know this, and you have problem with "unofficial" servers, just set everything manually (DNS, access point name) and don't use connection test.