Can anyone help me to figure out why my 'add to cart' button on collection page is not working?

Can anyone help me to figure out why my ‘add to cart’ button on collection page is not working?

I have set up this testing page to troubleshoot.

https://www.simpls.com/collections/discount-code-collections-all-except-bundles

The add to cart button displays correctly, but when clicked just continually shows a loading symbol.

I have a sneaking suspicion that it may be one of our apps that are interfering, but have no idea where to start diagnosing.

We would love to turn on the button on all the collection pages, but need it to work correctly.

Any help is greatly appreciated!