Listening to book on audible on iPad in car

I have listened to books many times using this device while driving. Today when I plug in iPad, I make device choice on radio (iPad) a notice Can not Use Accessory Only one accessory can be used at a time.

I have changed cords, turned everything off and on including the car, but nothing I do will allow my audible book to play. I listened to this book on my way to a family visit, but won’t work now. There are no other accessories attached