I don't even specify TuneIn - I can just say "play" followed by the name of the station, although Alexa can be very fussy about what you call it. For example, she won't play King FM Symphonic Channel unless I call it K-I-N-G, but when I ask her what's playing she says "King". She won't play BBC Radio London unless I add 94.9, but now she'll play it if I only say 94.9. It may be that she learns and that you have to ask for TuneIn on the first attempt for a station, but I think it's unlikely.