Add to cart button doesn't work when changing billing method

I have published my website but i have an issue.
I noticed that my website’s packages are on one time payment method and when i changed the billing method to subscription monthly. the add to cart button stops working. and i am not able to figure out why.

Can someone please help me out?
I made the premium monthly package a subscription based and the other two are one time payment method. so you can see the issue.

thank you! :)