Hi,

Please try to go to the file app\code\local\Sns\Ajaxcart\etc\config.xml, find and replace the code below

<!-- //ssl : https://
<secure_url>
	<ajaxcart>/ajaxcart/</ajaxcart>
</secure_url>
-->

By:

<!--  //ssl : https:// -->
<secure_url>
	<ajaxcart>/ajaxcart/</ajaxcart>
</secure_url>

to see whether the issue with add to cart from https has been solved.

Regards,