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Role Definitions

The ACK-Pay protocol defines several key components that interact to facilitate payments:

  • Client Applications and Client Agents: Software initiating service requests or payments on behalf of end-users or autonomous processes. In the Client-Initiated sequence, they are responsible for constructing the Payment Request.
  • Servers, Server Agents and Service Providers: Entities providing resources or services that may require payment and need to verify payment receipts before granting access or fulfilling requests. In the Server-Initiated sequence, they are responsible for generating and sending the Payment Request.
  • Payment Service: A crucial intermediary responsible for managing payment execution. Its functions can include:
    • Routing payments across different networks.
    • Assisting Clients in constructing Payment Requests (in Client-Initiated sequences).
    • Handling currency/asset conversions.
    • Interacting with underlying Settlement Networks.
    • Performing risk assessments and compliance verification (potentially using ACK-ID).
    • Managing human approval workflows.
    • Coordinating with Receipt Services.
    • Abstracting diverse payment methods, including traditional rails (ACH, card networks via APIs like Visa Intelligent Commerce or Mastercard Agent Pay), and blockchain networks.
    • Optionally acting as a bridge to other protocols by exposing compatible interfaces (e.g., functioning as an x402 Facilitator for servers using that approach).
  • Receipt Service: Generates and validates cryptographically verifiable receipts (typically as Verifiable Credentials), ensuring:
    • Secure credential issuance based on confirmed payment settlement.
    • Management of receipt status (e.g., validity, revocation).
    • Validation of presented receipts. (Note: The Payment Service and Receipt Service roles may sometimes be fulfilled by the same entity).
  • Settlement Networks: The underlying financial infrastructures that execute value transfer (e.g., traditional banking systems, card networks, blockchain networks).

These roles define the actors within the ACK-Pay ecosystem that orchestrate payment flows. The next section will explore how these actors collaborate with one another.

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Component Interactions with a Payment Service

The following component activity diagram illustrates a sophisticated flow involved a Payment Service.

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Component Interactions with Client-Executed Payments

The following component activity diagram illustrates a simple flow in which a Client Agent executes a payment directly via an embedded Payment Service.