How is the Integrator set-up different to PSP?

MobilePay Subscriptions is a solution, where the merchant enters an agreement with MobilePay regarding the usage of MobilePay solutions directly, which are not card payments, but MobilePay payments, which also explains why MobilePay stands for the payment flow. 

In this context, the merchant can choose to integrate our API directly, or to make use of the certified integrators, which can be found here

It is not like MobilePay Online, which is a payment card solution, where the PSP enter into an agreement about "borrowing" the card, that the MobilePay user already has registered in their MobilePay app to execute a purchase in a webshop. In this case, MobilePay does not have an agreement with the company.