We have a magento webshop (1.8.0), and sometimes we get messages from some of our customers that the add to cart button won't work.
Problem is: there's no error in the backend and it's on various operating systems and browsers (internet explorer, firefox and chrome). And not everyone has this problem, it's sometimes on chrome, sometimes on firefox, sometimes on internet explorer etc.
I have installed the browser versions and tried it myself; no problem.
I've set the cookie time to 86400 and correctly set the cookie domain and path.
Cookie path: /
Cookie Domain: http://www.domainname.com
I've checked if add to cart form had a form key, and checked the server time.
Checked the cookie also, if it contained the frontend value (read it somewhere).
I've had this problem before with the old template and Ipad2 users, and solved it by making a seperate template for Ipad2 users, but now I can't filter on user agents (too many browsers).
We're using magento 1.8.0 with the Ultimo Theme.
How can I debug this? Or any idea what to do?
I think I've got a clue what the problem is:
I accidently found out that if the wrong cookie_domain has been used, you cannot add anything to the cart. I filled in the wrong cookie domain on my localhost testing server and voila, the same problem appears.
Can't I just leave the cookie domain and path empty? Or what is the most universal solution, so I'm sure all browsers will work with it?