About your complain, I have checked your store and try and add to cart it is perfectly working fine.
But the one thing I noticed missing on your store is email marketing
Email marketing is the act of sending a commercial message, typically to a group of people, using email. In its broadest sense, every email sent to a potential or current customer could be considered email marketing. It involves using email to send advertisements, request business, or solicit sales or donations.
It is very critical and essential in e-commerce marketing and it will help you grow your business faster.
Don't know how to go about it?
Message me and I will guide you through.