Main Cause of The Problem
The download is impossible and the request is ‘forbidden’. This usually happens when two Google accounts are used to buy applications on one device.
Here Is How To Fix The Problem
Go the Google Play Store with the correct Google account. Uninstall the application in question. Try to get the app from Google Play again and click the purchase button.
Clear the proxy you have possibly set up, by going into the Settings, then choose Wireless and Networks (or More networks) and then Mobile Network. Select APN, which stands for Access Point Name and hit Clear Proxy Option. You can always reinstate the proxy afterwards.
Another solution would be to erase your entire search history which you can do in the Play Store itself by choosing the Settings button. Next, select the Clear search history.
Try creating a new Google account and using it instead for the Play Store. Go to the Google Play, and select the menu button again. Then select Accounts and choose the New Gmail account. Then reinstall the app.
Hope this little tutorial will help you fix this problem. Feel free to use the comment box for any complaint.