I checked your site again and I can now see the add to cart event firing correctly:
{
event: "gtm4wp.addProductToCartEEC",
ecommerce: {
currencyCode: "GBP",
add: {
products: [
{
name: "3D Moon Lamp The Most Unique Lamp",
id: "MLAMP20",
price: 24.99,
category: "Moon Lamp",
stocklevel: "0",
brand: undefined,
variant: "20CM",
quantity: "1"
}
]
}
}
}
Also I can see that a GA event hit is triggered on this GTM event. It includes proper enhanced ecommerce parameters:
pa: "add",
pr1nm: "3D Moon Lamp The Most Unique Lamp",
pr1id: "MLAMP20",
pr1pr: "24.99",
pr1ca: "Moon Lamp",
pr1va: "20CM",
pr1qt: "1",
Entering the checkout shows me the checkout action and data in your GA pageview hit.
Since I need to use by bank card to proceed to the order received page, I can not check this page for you but since every action is working correctly before that step, I assume this should work as well.
What you might also want to check is whether the auto return option in PayPal is turned on? By default, users are not forced to get back to your site after a successful payment which means that no transactions will be tracked towards GA.