Trying to install Joomla extensions and having the message "Warning: Failed to move file!". This article will give the solution for this error installation in your joomla website.
First solution
Check if in the main root of your joomla website, you have the folder tmp. To check it you may use FTP or file manager under control panel in your hosting.
If there is missing the folder tmp, simply create one. After make sure that the folder permissions is sett to 755. The Screenshot below shows the permissions in FTP.
It the folder /tmp was missing, after you create one, it should resolve the issue and the installation process should be fine.
Second solution
In Global Configuration check if the folder tmp has the correct path. This you can do it in configuration.php file of your website, by opening with text editor.
Other way is in Joomla Backend, go to System > Global Configuration and click in Server tab.
In "Path to Temp Folder" field, check if the link correspond the server path to your /tmp folder.
Third solution
In Joomla backend ( administrator panel ), go to System > System Information and click the "Folder Permissions" tab.
Check if the "Temp folder" is writable. If it is not writable, put folder permissions to 755 by following the info in the "First solution". By changing permissions to 755 the "Temp folder" will be writable. If any issues in doing this, contact your hosting provider.