Accessing line item details in Offsite Payment Extension

Extensions
1

I am currently implementing an Offsite Payment Extension for Shopify.

Our payment gateway requires detailed information about the purchased items, specifically:

  • Line item name
  • Unit price
  • Quantity
  • SKU (if available)

When Shopify initiates the payment session, I can access the payment session payload, but I cannot find the line item details.

My questions are:

  1. Is there a supported way for an Offsite Payment Extension to access the cart or order line items during the payment session?
  2. If not, what is the recommended approach to retrieve this information before redirecting the customer to our payment gateway?
  3. Is there any GraphQL API or webhook that can be used to obtain the purchased items while the payment is still in progress?
  4. If line items are intentionally unavailable during the payment session, what is the rationale behind this design?

Our payment gateway requires this information to display the purchased products on the payment page before the customer completes the payment.

Any guidance or recommended implementation would be greatly appreciated.

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