Google Playstore Wont

[R J Kinloch]

I can download Apps but they wont install.
I have a Xiaomi Mi Pad 2. It's running Android 5.1 LMY47I. Android Security Patch Level 2016-07-25 and MIUIGlobal 7.5l Stable 7.5.2.0 (LACCNDE)

Please Help!