I've found that playing music through a routine is very hit-and-miss.
For example, I created a routine to play iHeart 80's from iHeart Radio. Everything looks fine in the routine. But when running the routine, it just won't play or it plays the wrong playlist.
After many trials and errors, I discovered that the way you spell or enter the name of the song or playlist matters. And it matters A LOT! Even the spacing matters. "iHeart80s" is different than "iHeart 80s" when used in a routine. And both are different from "IHeart80s" with the capital I. For me, I had to enter the playlist exactly as "iHeart80s". If I entered it in any other variations on spelling, spacing, punctuation, or upper/lower case letters, the results will be different.