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[mesnitu]

I don't know how to find the debug logs.

They should be in your /logs folder.
There's a similar thread on this , and reading it, actually this product doesn't have the www like the others.
Maybe you can find a solution in there

https://www.zen-cart.com/showthread....-You-are-still

[lat9]

Echoing @mesnitu's response, it looks like the issue is when the customer navigates to your site without the www. prefix. Your store's configure.php file appears to use www.yourstore.com as the server and you don't have an .htaccess file to re-direct a www-less (e.g. yourstore.com) access to its www-with form.