Hey! I got it to work!! I found this on CF7's website. I tried it with my paypal button. There are NO Parentheses at all.
http://contactform7.com/redirecting-to-another-url-after-submissions/
My string looks like this:
on_sent_ok: "location = 'https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=[PUT YOUR BUTTON ID HERE]';"
Place your button id in place of the [PUT YOUR BUTTON ID HERE]. Make sure box brackets are not there.
Also, it is slow to process. I'm not sure if it is my server that is slow or the redirect. However, it DOES work!