Distinguish line items created by "Subscription app Shopify"

[BillyND]

Hello everyone, I am working on a major project to build a subscription app shopify. I have successfully created the sellingPlanGroups and sellingPlans.

I have registered webhooks to receive ORDERS_CREATE and SUBSCRIPTION_CONTRACTS_CREATE.
Please tell me how to differentiate the line items ordered by subscriptions created by my app?
I have tried using properties to set a distinguishing flag, but it doesn't work with "Buy now" and the information becomes incorrect if the user deletes the properties in the order.

Thank you very much. Please help me!