Okay I changed it and now its going to the shopping cart but it's not going back if the product isn't available or it's not reflecting the product options like it was doing before. The options like color size etc aren't being remembered.
I've uploaded the last working version you can see that it works.
https://www.familyfriendlystore.com/products-detail.php?ProductID=1001 doesn't work.
The difference between the 2 is I added the UD1, UD2, UD3 options.