Sorry for the long reply time, I started my year mostly today ??
I’ve checked your sandbox site and I can see the data layer. For some reason, on your homepage a product click event is also fired but without product data. This has to be connected with some other JS code on your site, perhaps in your theme.
Product clicks on list pages do not pickup product data: this is again some incompatibility with your theme since I can not see the meta data added by my plugin in the HTML code of a list page. You (or your dev) can check here what WooCommerce/Storefront codes need to execute in order to properly track product lists as well as other WooCommerce pages:
https://gtm4wp.com/how-to-articles/how-to-make-your-wordpress-theme-compatible-with-enhanced-ecommerce-tracking
The add to cart event is working properly on product detail pages.
I can also see the checkout data layer as well.
Since I had to pay for the goods in your shop with my credit card, I was not able to check your “order received” page but from what I can see it should work as well.