AptURL is required
The AptURL Protocol Handler and a Web browser support are required to install applications. The AptURL Protocol Handler is a program that handles special URLs to installing software on APT-based Linux systems. Ubuntu 7.10 or higher can use AptURL by default.
Please install the package “apturl” if using APT-based Linux systems like Debian, Linux Mint, PCLinuxOS.
Install from Synaptic Package Manager
Go to Synaptic Package Manager and find “apturl”.
When you have found it check it and click on “Apply Changes”.
Install from Terminal
sudo apt-get install apturl
After installing apturl you need to visit the Appnr select the category and then application now you need to click on Install that's it it will install your application.