Bluetooth connected to car stereo but no sound

I've always been able to listen to music and podcasts on my iPhone by connecting my iPhone to my Prius via bluetooth and listening to it over the car's audio system. I've never had a problem with this. Until today. 

Today, all of a sudden, my car no longer plays my iPhone audio over the car's audio system. It's really weird. My car recognizes my Iphone. It says it is connected via bluetooth. When I play songs, it shows them on the car audio display. I can even use the car's audio controls to change songs. However, no sound actually comes out of my car's speakers. While the car shows the phone as connected, the sound is all coming from the phone, not the car. 

By contrast, when I play the radio, the sound comes out of the speakers just fine. 

I tried restarting both my phone and the bluetooth and my car but none of these things works. And i have also factory reset my phone but still having same issue.