Bluetooth sound not working on car!

[xykudyax]

I'm using latest version of iOS 11 and I have a bluetooth device installed in my car the bluetooth works great with calls and also stock applications VoiceRecorder and Apple Music app over the bluetooth. when using 3rd party apps such as Spotify there is not sound. The connection is established... no sound comes from the iPhone... but, no sound comes from the car radio either.
What can I do?!

[Charity13]

I have the same issue since updating to IOS 11. No idea how to fix it?

[regalrecaller]

Same with Android 7.0

bumping this thread for shameless exposure to this question so I can maybe figure out how to make my bt device play spotify again.