not able to install

Hi,
I’m trying to install WP Fastest cache.
I got the message that my .htaccess was not writable, so I manually put the code in my .htaccess, as instructed. I also had the error message that the directories -/wp-content/cache and -/wp-content/cache/all were not present. I manually created them, and set the permissions to 755 as instructed.
Still, when I click submit, I am prompted again to change my .htaccess and set the permissions of /cache and /cache/all to 755. But the .htaccess is already changed, and the permissions are already set to 755.
What could be the problem?
My website is http://www.fasol.nl.

Thanks

Peter

https://ww.wp.xz.cn/plugins/wp-fastest-cache/