diff --git a/a2a/business_agent/src/business_agent/agent.py b/a2a/business_agent/src/business_agent/agent.py
index 4caeea8..3b8bec7 100644
--- a/a2a/business_agent/src/business_agent/agent.py
+++ b/a2a/business_agent/src/business_agent/agent.py
@@ -293,9 +293,10 @@ async def complete_checkout(tool_context: ToolContext) -> dict:
         "status": "requires_more_info",
     }
 
+  payment_instruments = payment_data.get(UCP_PAYMENT_DATA_KEY).instruments
   try:
     task = mpp.process_payment(
-        payment_data[UCP_PAYMENT_DATA_KEY], payment_data[UCP_RISK_SIGNALS_KEY]
+        payment_instruments, payment_data[UCP_RISK_SIGNALS_KEY]
     )
 
     if task is None:
@@ -304,9 +305,7 @@ async def complete_checkout(tool_context: ToolContext) -> dict:
       )
 
     if task.status is not None and task.status.state == TaskState.completed:
-      payment_instrument = payment_data.get(UCP_PAYMENT_DATA_KEY)
-      checkout.payment.selected_instrument_id = payment_instrument.root.id
-      checkout.payment.instruments = [payment_instrument]
+      checkout.payment.instruments = payment_instruments
 
       response = store.place_order(checkout_id)
       # clear completed checkout from state
diff --git a/a2a/business_agent/src/business_agent/agent_executor.py b/a2a/business_agent/src/business_agent/agent_executor.py
index a7e708e..08b51b4 100644
--- a/a2a/business_agent/src/business_agent/agent_executor.py
+++ b/a2a/business_agent/src/business_agent/agent_executor.py
@@ -28,6 +28,7 @@
 from google.adk.runners import Runner
 from google.adk.sessions import InMemorySessionService
 from google.genai import types
+from ucp_sdk.models.schemas.shopping.payment_create_req import PaymentCreateRequest
 from ucp_sdk.models.schemas.shopping.types.payment_instrument import PaymentInstrument
 from ucp_sdk.models.schemas.ucp import ResponseCheckout as UcpMetadata
 from .constants import (
@@ -176,7 +177,7 @@ def _prepare_input(self, context: RequestContext) -> tuple[str, dict | None]:
         if key in data_part:
           value = data_part.pop(key)
           if key == UCP_PAYMENT_DATA_KEY:
-            payment_payload[key] = PaymentInstrument.model_validate(value)
+            payment_payload[key] = PaymentCreateRequest.model_validate(value)
           else:
             payment_payload[key] = value
 
diff --git a/a2a/business_agent/src/business_agent/constants.py b/a2a/business_agent/src/business_agent/constants.py
index 7fe95bb..2e2c1ee 100644
--- a/a2a/business_agent/src/business_agent/constants.py
+++ b/a2a/business_agent/src/business_agent/constants.py
@@ -28,5 +28,5 @@
 UCP_DISCOUNT_EXTENSION = "dev.ucp.shopping.discount"
 
 UCP_CHECKOUT_KEY = "a2a.ucp.checkout"
-UCP_PAYMENT_DATA_KEY = "a2a.ucp.checkout.payment_data"
+UCP_PAYMENT_DATA_KEY = "a2a.ucp.checkout.payment"
 UCP_RISK_SIGNALS_KEY = "a2a.ucp.checkout.risk_signals"
diff --git a/a2a/business_agent/src/business_agent/payment_processor.py b/a2a/business_agent/src/business_agent/payment_processor.py
index 4142fa1..837c60c 100644
--- a/a2a/business_agent/src/business_agent/payment_processor.py
+++ b/a2a/business_agent/src/business_agent/payment_processor.py
@@ -23,7 +23,7 @@ class MockPaymentProcessor:
   """Mock Payment Processor simulating calls from Merchant Agent to MPP Agent."""
 
   def process_payment(
-      self, payment_data: PaymentInstrument, risk_data: Any | None = None
+      self, instruments: list[PaymentInstrument], risk_data: Any | None = None
   ):
     """Process the payment."""
     # this should invoke the Merchant Payment Processor to validate the payment
diff --git a/a2a/chat-client/App.tsx b/a2a/chat-client/App.tsx
index a7081b8..4a7ea3d 100644
--- a/a2a/chat-client/App.tsx
+++ b/a2a/chat-client/App.tsx
@@ -20,7 +20,7 @@ import Header from './components/Header';
 import {appConfig} from './config';
 import {CredentialProviderProxy} from './mocks/credentialProviderProxy';
 
-import {ChatMessage, PaymentInstrument, Product, Sender} from './types';
+import {ChatMessage, Payment, PaymentInstrument, Product, Sender} from './types';
 
 const initialMessage: ChatMessage = {
   sender: Sender.MODEL,
@@ -167,13 +167,16 @@ function App() {
       userActionMessage,
     ]);
 
+    const payment: Payment = {
+      instruments: [paymentInstrument]
+    }
     try {
       const parts = [
         {type: 'data', data: {'action': 'complete_checkout'}},
         {
           type: 'data',
           data: {
-            'a2a.ucp.checkout.payment_data': paymentInstrument,
+            'a2a.ucp.checkout.payment': payment,
             'a2a.ucp.checkout.risk_signals': {'data': 'some risk data'},
           },
         },
diff --git a/a2a/chat-client/types.ts b/a2a/chat-client/types.ts
index dfa2cf1..bbc8f4f 100644
--- a/a2a/chat-client/types.ts
+++ b/a2a/chat-client/types.ts
@@ -55,6 +55,10 @@ export interface PaymentInstrument extends PaymentMethod {
   credential: Credential;
 }
 
+export interface Payment {
+  instruments: PaymentInstrument[];
+}
+
 export interface ChatMessage {
   sender: Sender;
   text: string;