The ones you see, they are already in setti master list or any other paid master list, which is compatible with their game client build.
You cannot add new servers to setti at the moment. It's unknown when the master server of setti goes online/offline. You will have to verify that every week.
If the master server is online, make sure the setti bot is able to connect to your server when you add the server to setti. When you add the server, the response should be "Server accepted me." Even if the response is successful, it is not guaranteed that your server will show in the old game client. Because you have no control over how master server works with the old game client.