Why you can't install joomla 3 extensions
This is a very common question from our clients telling us that they are unable to install an extension on their Joomla 3 website.
If you get warning message such as “could not create directory” or “warning! failed to move file” – in other words, Joomla was unable to install your plugin. Don't be panic please check these following reasons:
Wrong paths to the tmp and log in your configuration.php file
You should check if "logs" and "tmp" directories are selected properly. You can check correct path in Cpanel >> File Manager
Unable to write to the /tmp directory
In PHP (which is the programming language that Joomla is written with), usually when you upload a file (unless you change the php.ini file), it is uploaded to the /tmp directory. Now if Apache can’t upload to this directory (due to permission problems) then your extension won’t be uploaded, and thus won’t be installed. The solution to this is to create the /tmp folder and ensure that Apache and your account both have write permissions on this folder.
Zip library not installed on PHP
All the Joomla extensions are zipped when they are in the installable format. At one point, when you are installing an extension, Joomla needs to unzip it in order to move it to the appropriate folder(s). If the zip library is not installed, then Joomla won’t be able to install the extension. The solution to this problem is to contact your system administrator to install the zip library on PHP (note that Apache needs to be restarted once the zip library is installed).
PHP file upload size is too small
The solution is to modify php.ini file with the command to increase upload max size