Zend certified PHP/Magento developer

Magento add to cart in sub domain not working

I have configured a staging environment from the live environment. I have completely copied all files and the exact database of live and configured staging. But, the issue is I can add to the cart in a live environment as well as a development environment not in a staging environment. The staging environment is a subdomain of the live environment. I suspect the same domain issue but no error logs found.

  1. When clicking on add to cart the ajax call is loaded
  2. Then it shows like Added but not added

I also added cookie domain and checked no use.