because all the posts about this topic refer to this.
I get to this part
"3. If you have different domains, in this case you can add session ID to the URL for another store. Use this construction "Mage::getModel('core/url')->addSessionParam()->getUrl('...')" to get the URL with session parameter."
I'm not sure where to add this. I tried putting it in configuration, web, base url, and my site looped about 500 times, until I went into phpmyadmin and removed it.
I also did this part
Copy this file: app/code/core/Mage/Checkout/Model/Session.php to: app/code/local/Mage/Checkout/Model/Session.php.
and made the edits as specified, but all I get is a blank page. How do I see the magento store id so I can "Change CHECKOUT_STORE_ID value "1" to your Magento store ID with all products."?