Module 2: Communication
Steps 1 to 3 in the Bundesbank flow. Layer: communication. Actors: the customer, the AI agent, the merchant and the gateway.
Module 1 ended with a mandate: a grant of authority the agent holds and a payment service provider can check. Module 2 asks a plainer question. Now that the agent is allowed to act, how does it reach anyone? A mandate to buy groceries is worth nothing if the supermarket's systems cannot be found, read or called by software.
By the end of this module you will be able to:
- Walk steps 1 to 3 of the Bundesbank flow and say which actor talks to which, through what
- Explain why the Bundesbank calls the communication layer the gatekeeper, and what "an agent can only use what has been exposed to it" means in practice
- Describe what MCP and A2A each do, and what they do not do, for a payment
- Read a merchant's agent-facing surface (robots.txt, llms.txt, a UCP profile, an agent card) and say what an agent can reach
- Explain why control of the integration point is where the Deutsche Bundesbank expects market power to collect
Three steps, three conversations
In the stylized flow, three things happen between the mandate and the first payment decision.
Step 1 is the only one of the three that involves the person. The customer says what they want. In the Bundesbank's full-autonomy case the purchase order can be as thin as "keep the kitchen stocked", with the mandate from Module 1 supplying the limits. In a low-autonomy product it is a specific basket. Either way, the order is an instruction to the agent, not to any merchant.
Step 2 is where the agent first touches the outside world. It searches, compares and selects. The Bundesbank colors this step as decision-making, and Module 3 takes the decision apart. For this module the point is narrower: the agent can only select from merchants and products it can reach and read. Whatever the merchant has not exposed in a form software can parse is, for the agent, not for sale.
Step 3 is a conversation the agent is not party to. The merchant delegates checkout to a gateway, the technical service provider that will offer payment methods and accept the payment. From here the agent deals with the gateway, not the merchant, for everything to do with paying. That hand-off decides which instruments the agent will be offered at step 4.
An agent can only use a payment instrument that has been made available to it through an interface or a protocol. Everything else does not exist, as far as the agent is concerned.
Why the Bundesbank calls this layer the gatekeeper
The Bundesbank's architecture chart draws the communication layer as the outer frame around decision-making, execution, authorization and identity. It is the integration point. It makes payment operations available to agents at a technical level and determines how they are called and controlled.
Two things follow from that, and the Bundesbank names both.
Access control. Since agents can only use what is exposed, whoever decides what is exposed decides what agents can do. That is true of the merchant (which products, which checkout), the gateway (which payment methods), and the platform the agent runs on (which tools, which protocols).
Operational translation. The layer is also where upstream decisions become concrete payment operations. The agent's choice has to be turned into a call something will act on. The Bundesbank's phrase is that this combination of access control and operational translation gives the layer its particular strategic importance.
The actors the Bundesbank places here are technology corporations, AI providers and cloud and infrastructure providers. Not payment service providers. That placement is the market-structure argument of this module in one line, and the third lesson comes back to it.
What I measure every Saturday
The Bundesbank's claim is about architecture. It is also testable at the merchant end. Every Saturday I scan the 92 largest US storefronts for the four things an agent would need to find in order to reach them at step 2: a robots.txt that does not withhold itself, a homepage an agent can read, an llms.txt, and a published protocol profile such as a UCP profile or an A2A agent card. The results are on the merchant readiness tracker, and the first run is written up in The Front Door Nobody Was Watching.
The October 17 run found 31 of the 92 withholding robots.txt from agents, 46 with a homepage an agent could read, 15 with an llms.txt, three with a UCP profile and one with an A2A agent card. Read those figures against the three steps above. For most of the 92, step 2 is not possible yet by any published route. The gatekeeper is shut, not because of a policy decision but because nobody has opened it.
Next lesson: MCP and A2A, the two protocols the Bundesbank puts at this layer, and what each one does for a payment.