@The_Picard_Maneuver I once bought a TV sound bar that wanted me to download an app, make an account and give it detailed location information just to use it as a wired speaker. I returned it.
If there's a tape deck, you can do headphone jack to cassette tape. If you don't have a headphone jack on your phone you can get a little bluetooth reciever to headphone jack type thing.
There's also the route of using a small device to broadcast your own little AM station (same deal, gets audio from jack or bluetooth), then tune into it with your existing head unit.
Best way is to just rig up your own aux in, but that requires some doing.
Was it a Bose? I once bought Bose headphones and downloaded an app to pair it. When Bose recognized the headphones, it told me that I had used the wrong app to pair to those headphones.
@snow_bunny Nah, it was Sonos. Which, I guess the app ecosystem is their whole thing - but I didn't know that at the time. I just wanted a basic sound bar, and the reviews didn't really mention that all that extra fluff was mandatory.
In retrospect Sonos sucks for a lot of other reasons too, so I guess it was a bullet dodged.