TuneIn Radio Support on Homepod Mini - Sometimes requires iPhone

I use my Homepod daily in my store to play TuneIn Radio. I find that often the Homepod says that it requires the iPhone to connect to the requested channel ("I am having trouble connecting to your iPhone" or "I need to connect to your iPhone to play TuneIn Radio"). This experience is inconsistent in that it will give this message on one channel however not on another, and then if I retry the same channel again, it may work the second (third, fourth...) time.

The problem seems more common on certain channels, while others never have the issue, however I can not find any real pattern.

As I come and go from the store with my phone, I need the Homepod to be independent and not tethered to my phone for music.

What is the trick here? Or is there some logic to this?