I'm developing an offsite payment gateway for Shopify, and I would like to obtain the cart data for the payment (which is not directly sent from Shopify to the gateway). There is a solution in this post, which is based on the checkout webhook. However, this other post warns about assuming real-time-ness from webhooks, which is problematic, because I need to be sure to have the checkout data as soon as the payer is directed to my gateway.
Another potential solution that I have found is using the Admin API to fetch the the Abandoned Checkouts and identify the one corresponding to the payment by matching it with the reference sent to my gateway. I've tested it with a test store and it seems to work. My question is : How reliable that is? Can I be sure that when the payer is directed to my gateway, its checkout is currently available in the "Abandoned Checkouts" resource?