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Hence, it would be more accurate to define the card processing as being the business logic that is stable whatever the merchant environment that will integrate it. And the stability of the “L2” is crucial in the context of terminal approval processes managed by payment networks.
This definition leads us to three distinct perspectives of the card processing, a.k.a. the Level 2:
Its certification
Its integration
Its maintenance
Certificability, Integrability, and Maintainability are 3 important concepts to address the card processing.