Send quantity and dynamic succes url to Stripe

Following up on Teodor’s tutorial on Stripe checkout with custom products:

How can I send the right quantity to Stripe? I tried to get it through the query, although I am quite sure that doesn’t make sense because it’s stored in the data store instead of the products db table:

How can I get the quantity value from the lineItems array per line and pass it on to stripe?

Also I would like to know how to set the success_url (if set in AC Stripe element as dynamic attribute)
as a dynamic value to the SC Create Checkout Session? I tried using a variable calles succes_url (see screenshots below), but that didn’t work. What’s the right variable name to use in the SC for this dynamic attribute?

Thanks for any help in advance.