If the iPhone doesn’t have any songs downloaded to the Apple Music app any form of media won’t play through the usb. Usually when the iPhone is plugged in through the usb it will default to playing through the music app then you have to switch it over to Spotify. Without that default play through, it will deny all media through the usb. At least that’s how it works in my 15 silverado. Sent from my iPhone using Tapatalk