It's supposed to make payments easier with a Stripe-hosted payments page. However, creating a server-side Checkout session, and then getting line items from an order, is an unnecessarily convoluted series of requests.
You can use "expand" to get multiple queries into a single request, kind of like a SQL join. I don't know if this is exactly your use case, but when we get a Checkout session, and want the customer and purchase line items, it looks like this (using the Stripe Ruby library).
https://stripe.com/payments/checkout
It's supposed to make payments easier with a Stripe-hosted payments page. However, creating a server-side Checkout session, and then getting line items from an order, is an unnecessarily convoluted series of requests.