BMW iPhone 6+ Snap-in Adapter Question

I got a 2010 BMW E70 X5d. After loading lots of mp3s on my iPhone 6+ and connect it to my car via Y-connector and "30-pin to lighting adapter" combo, didn't play music. The car wouldn't recognize the phone, and each time I plugged it in, my phone always asked me whether to "trust this computer or not." After I touched "trust", my car still wouldn't recognize the phone. My iPhone 4S could play music, my Nexus 5 could play music. Thus I don't understand why this iPhone 6+ couldn't play music. Has anyone else encountered this issue? If so, may I know how you solved it?

Anything helps, thanks. : )