You’re using the wrong endpoint. Search is for when you want to search for channels that match in part or whole your query, but you already know the specific channel so don’t need to search.
If you want to see if a channel is online you should use the Get Streams endpoint https://dev.twitch.tv/docs/api/reference#get-streams which will return an empty array if you’re offline, or the stream object for the channel if you are online.