cannot install smush wp pro on my site 40plusstylecourses.com

I cannot install wp smush pro

I get this message.

Installation of WP Smush Pro failed. Most likely reason for this are wrong folder permissions of your wp-contents folder.

I gave the wp content folder 755 permissions (is that not unsafe?)

But even after that no luck.

A search on this site did not come up with any answers.