Garmin Zumo GPS

I sometimes drive on remote country roads over my own routes, not ones jiggered for me by Google Maps or whatever. I save my routes on a Garmin Zumo GPS unit. I can use them on Prius by pairing them with Bluetooth (the car has no Entune). The pairing works except the Prius doesn't play the Zumo's turn directions. It plays the Zumo's music but not the turn directions. Instead, there's a silent period for the few seconds the directions should play.

Is this a known problem with third-party GPS units?

PS
Yes, I'm asking Garmin about this, too.