It means you're not allowed to download the game via Google Play Store from your current location. For example: This game is released in Vietnam but you're in USA now. In this case, you can follow one of these steps to download and install game from the APK file.

• Step 1: Open any browser: Google Chrome, Mozilla Firefox, Opera, Internet Explorer…
• Step 2: Access on Google Play Store via https://play.google.com/store and find the game/app you want to download.
• Step 3: Click on the game/app you want to download.
• Step 4: Copy URL address that you used opened.
• Step 5: Access on http://apps.evozi.com/apk-downloader/ and paste the link from Step 4 into the blank field.
• Step 6: Click the button GENERATE DOWNLOAD LINK
• Step 7: Wait for some minutes, until the button CLICK HERE TO DOWNLOAD appears, click it.
• Step 8: The selected app will be downloaded automatically to your PC.
• Step 9: Copy downloaded file to your Android device and install. All Mobgame games also have download links for APK files on Homepage or Fanpage

You can download and install directly on your Android device from this download link. Use VPN OneClick

• Step 1: Download and set up VPN OneClick from Google Play via link https://play.google.com/store/apps/details?id=com.vpnoneclick.android
• Step 2: Open app VPN OneClick and select 1 server you want to connect (eg: Canada, Usa…)
• Step 3: When connected, your screen will show IP address and the country you're using to login.
• Step 4: Delete Cache of Google Play Store 
  Go to Settings >> Apps >> All >> Google Play Store
  Click Clear Cache
• Step 5: Open Google Play and install games