If your voice command won't find a radio station in TuneIn which you knowis there, then you can go into the Alexa app and choose it from TuneIn manually.
I am not sure of the best way to launch the TuneIn station list within the Alexa app but the way I do it is to go to the voice command history (using the Home button at the bottom) and find a previous TuneIn station I started previously. There is a link there to launch the TuneIn station list within the Alexa app.
Is there an easier way than this, anyone?
The station starts playing on the Echo speaker as soon as it is touched in the radio station list.