The on-demand or offline discovery process can be used by PSPs that wish to onboard to Microsoft would be to use the publicly-accessible payment method discovery service to query the list of supported payment methods, along with additional information about what is supported for each payment method, enrollment information, payloads, etc.
Async Notification Service
Some transaction and enrollment calls are asynchronous by nature and require a callback from PSP to Microsoft to notify when an operation concludes. All async notifications should be sent with a client certificate which uniquely identifies the PSP.
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