This usually occurs if you are playing on an older device that is no longer supported by the game.

Also, for some high end Android devices, resolution might wrongfully cause a device to appear incompatible. In these cases it is likely that the device resolution has been lowered below a resolution that is required by the game.

If Google Play says "device not compatible", please attempt resetting your device resolution to Mid or High in "Device Settings". Go to your Settings ->Display-> Screen Resolution, and change the resolution. This should take care of the issue.