First of all, can any other devices you have get this TuneIn station? Try getting the station that way to see if same issue exists. Secondly, look up station at TuneIn.com and find the station. Can It be played in your browser? Often, stations change their name slightly and that can cause an issue, so get exact name.
I have my best success by prefacing my Alexa tunein requests by saying, Alexa play tunein station XXX (e.g. Jazz Wyoming; sometimes call letters don't work, especially if there are more streaming stations using the call letters (saying KUWL does not get the jazz station.) This is often the case with streaming-only stations. You could also check the station website for info, too.
Basically, you have asked a TuneIn question and not a Tap or Alexa question. You just have to get the station name correct, and it appears you haven't, so Alexa is "stumped". I hope this post helps you for looking in the right direction for your answer.