If you just downloaded an app for Android from the Google Play Store and while installation the app you get an error message saying : Device not compatible
then follow the below steps to resolve this issue.
1. Go to Settings App
2. Select Application Manager
3. Select All
4. Select Google Play Store
5. Now Clear Cache.
Now try downloading/upgrading the App and you may not face this issue.
What causes this issue
One of the reasons can be that you just changed the DPI resolution for your device, which the app maybe not compatible with.