Due to the new Google Consent Mode requirements, I have no choice but to integrate Klaviyo into Shopify using Google Tag Manager.  The Shopify integration does not respect consent mode unfortunately.

Most things look easily doable but one part of the integration is confusing me

In Shopify we have no access to checkout code, so cannot hook into the checkout page. How do we get the product data that is in the checkout if I cannot fire any code in the checkout?

I have seen a few articles that mention to send the data when the checkout button is clicked.  That would mean we would have to send the data from the cart, is that correct? A potential issue here is being able to enter the checkout when not in the cart - we have a mini-cart that is accessible on all pages.

An issue with that approach if it is recommended, is that we cannot identify the customer at that point as a guest would not have entered their email address whilst still in the cart.

A little unsure about how to implement this.  Hopefully the above is clear.

Thanks,
Simon