Local files won't play when using Bluetooth

[VioletHughes]

I've added a few songs (local files) to my Spotify play lists, using my PC and synching with my iPhone. These songs play when I'm listening directly to Spotify on my phone (which I never do but I tried it just to check this issue out), but will not play when I've got headphones plugged in, or streaming on Bluetooth. How do I fix this so that these songs are included on the playlists regardless of how I'm listening to them?