I assume that you have connected and wired the device correctly (use the correct adapter if necessary).
If so, you need to press and hold the music button a little longer to switch it off.
Regarding the DAB transmitter: Install the Smart Sync app and read the operating instructions.
P.s.
Depending on the smartphone, some functions may not work properly.

- This device has been installed in an 18-year-old Polo for several months and works perfectly with an iPhone 15 and an Android 14 device.

This thing is crap. I can't even record preset DAB stations.