Issue with Ipad Pro USB-C dongle to lighting headphones

I have an ipad pro with usb-c port. My Bose Quiet Comfort headphones have a lightning connector (noise cancelling, self powered with a battery). I bought a dongle that is USB-C male to lightning female so they are connected. When play anything on the ipad, sound still comes only from ipad speaker just as if nothing at all was plugged into the UBC-C port at all? Any ideas please? thanks in advance.