How does a cashback service and an offline store interact?

Question

Electronic commerce

I am doing a diploma on the development of a cashback service for checks. And I can’t figure out how the cashback service and the offline store interact. In online cashback, the buyer buys goods through the cashback service, the store pays a percentage of the purchase to the cashback service after the completion (delivery) of the order, then the cashback service shares the percentage with the buyer.
In offline cashback, the customer scans the QR code on the check in the cashback service application, after which the cashback service checks the authenticity of the check, but what happens next?