Have you bought your new MiPad or Mi4 and is not able to use Messenger properly? The chat heads are not working? Then you are at the right place. MIUI 6 gives you a lot of of permissions over your apps and this makes some apps not working properly so here are the steps-
1) Got to Settings.
2) Go to Apps option in the list.
3) Navigate to Messenger in the list.
Now when you are on the Messenger properties, you will find a option Allen “Turn on Floating windows” and toggle it.
4) Voila! Messenger would be now working as it should.