This is how to pair your iPhone or Android phone to a 2003 Ford Fiesta. Generally, pairing a Bluetooth compatible phone to your car will allow you to make handsfree calls. In many models, you can also play music through a paired device over the Bluetooth connection too. Check your owners manual to see if this is possible in your 2003 Fiesta.
Same issue with me on My Ford Fiesta. Worked fine yesterday with 8.1.2, upgraded last night to 8.1.3 and no music plays through the car speakers. I tried everything including the Master Reset and restoring the iPhone. I really wish I hadn't left it late to upgrade to 8.1.3 as now there is now no possibility of downgrading. As a dirty workaround I launch manually spotify, start my car, and use blutooth headset mode, but to change artist, album, whatever, I have to check my phone. I'll check for an older apk. Galaxy Note 2, android 4.4.2, spotify v7.0.0.1369, Fiesta 2016.