Plugin Download failed. Forbidden

Hello,

This issue happens in particular cases and is tied to specific server and php configuration. There are a few steps in solving this issue however.
1. Check file permissions: http://www.wpbeginner.com/beginners-guide/how-to-fix-file-and-folder-permissions-error-in-wordpress/
2. change php version on your host and check security modules.
3. comment out the check for the error from the wordpress code:
https://scotty-t.com/2011/03/28/fix-for-the-plugin-does-not-have-a-valid-header/
4. Install the plugins via ftp: http://www.wpbeginner.com/beginners-guide/how-to-manually-update-wordpress-plugins-via-ftp/

Hope this helps.

Thank you!