Question about Mi 2 - 387608

I wanted to use the headphones with a Samsung Galaxy S9+. I can establish the Bluetooth connection, but nothing happens. No music in the headphones and no response to other functions. It seems the phone doesn't recognise the headphones as such. Do I need to set anything else? Are the headphones compatible with Samsung phones at all? (There's nothing in the manual and I haven't found anything else either).