How can I listen to audio on Android with a Mono Bluetooth Headset ?

A Mono Bluetooth Headset

What I want to do :
Listen to audio on an android phone though a Bluetooth Mono headset

Problem :
My mono bluetooth heasdset is paired with my Android device but I cannot listen to music. It only works for phone calls

Answer :
You need an app from Google Play.
I am using free  'Mono Bluetooth Router' but there are alternative apps 

Instructions :
Pair up the headset with the Android device (e.g. phone/tablet)
Download an app via your Android device from Google Play (for me : 'Mono Bluetooth Router' )
Find the app icon on your phone. Click it and press 'connect'
If the headset and device are paired and you have bluetooth switched on, it should work  

Do stereo bluetooth headphones need an app to play on an Android device ?
Answer : I don't seem to need one. My stereo headset works fine and the sound quality is much better. 

Note :
The sound is very poor but it works. I might try other apps to to see if it's to do with the app but I think it's the headset that is the problem. 

It seems to be an Android quirk that mono bluetooth headsets need an app to play audio on Android devices. They work ok for phone calls though.