diff --git a/packages/atxp-client/src/mppProtocolHandler.ts b/packages/atxp-client/src/mppProtocolHandler.ts
index 8b861b8..d18c006 100644
--- a/packages/atxp-client/src/mppProtocolHandler.ts
+++ b/packages/atxp-client/src/mppProtocolHandler.ts
@@ -189,6 +189,9 @@ export class MPPProtocolHandler implements ProtocolHandler {
       }
 
       const retryHeaders = buildPaymentHeaders(authorizeResult, originalRequest.init?.headers);
+      if (primaryChallenge.id) {
+        retryHeaders.set('X-ATXP-Payment-Request-Id', primaryChallenge.id);
+      }
       const retryInit: RequestInit = { ...originalRequest.init, headers: retryHeaders };
 
       logger.info('MPP: retrying request with Authorization: Payment header');
diff --git a/packages/atxp-client/src/protocolHandler.test.ts b/packages/atxp-client/src/protocolHandler.test.ts
index 5f2ca9a..e445d1f 100644
--- a/packages/atxp-client/src/protocolHandler.test.ts
+++ b/packages/atxp-client/src/protocolHandler.test.ts
@@ -98,7 +98,10 @@ describe('X402ProtocolHandler', () => {
 
   describe('canHandle', () => {
     it('should detect X402 challenge in 402 response', async () => {
-      const response = new Response(JSON.stringify(createX402Challenge()), { status: 402 });
+      const response = new Response(JSON.stringify({
+        ...createX402Challenge(),
+        paymentRequestId: 'pr_x402_retry',
+      }), { status: 402 });
       expect(await handler.canHandle(response)).toBe(true);
     });
 
@@ -140,7 +143,10 @@ describe('X402ProtocolHandler', () => {
         onPaymentFailure: async () => {},
       };
 
-      const response = new Response(JSON.stringify(createX402Challenge()), { status: 402 });
+      const response = new Response(JSON.stringify({
+        ...createX402Challenge(),
+        paymentRequestId: 'pr_x402_retry',
+      }), { status: 402 });
       const result = await handler.handlePaymentChallenge(
         response,
         { url: 'https://example.com/api' },
@@ -159,6 +165,7 @@ describe('X402ProtocolHandler', () => {
       const retryCall = mockFetch.mock.calls[0];
       const retryHeaders = retryCall[1].headers as Headers;
       expect(retryHeaders.get('X-PAYMENT')).toBe('test-payment-header');
+      expect(retryHeaders.get('X-ATXP-Payment-Request-Id')).toBe('pr_x402_retry');
 
       // Verify onPayment was called
       expect(mockOnPayment).toHaveBeenCalled();
@@ -559,6 +566,7 @@ describe('MPPProtocolHandler', () => {
       const retryCall = mockFetch.mock.calls[0];
       const retryHeaders = retryCall[1].headers as Headers;
       expect(retryHeaders.get('Authorization')).toBe('Payment mpp-credential-base64');
+      expect(retryHeaders.get('X-ATXP-Payment-Request-Id')).toBe('ch_xxx');
 
       // Verify onPayment was called
       expect(mockOnPayment).toHaveBeenCalled();
diff --git a/packages/atxp-client/src/x402ProtocolHandler.ts b/packages/atxp-client/src/x402ProtocolHandler.ts
index 0a8f647..df24e08 100644
--- a/packages/atxp-client/src/x402ProtocolHandler.ts
+++ b/packages/atxp-client/src/x402ProtocolHandler.ts
@@ -26,6 +26,7 @@ interface X402Challenge {
   /** v2 adds resource info and extensions */
   resource?: { url: string; description?: string; mimeType?: string };
   extensions?: Record<string, unknown>;
+  paymentRequestId?: string;
 }
 
 /**
@@ -156,6 +157,9 @@ export class X402ProtocolHandler implements ProtocolHandler {
         { protocol: 'x402', credential: paymentHeader },
         originalRequest.init?.headers
       );
+      if (paymentChallenge.paymentRequestId) {
+        retryHeaders.set('X-ATXP-Payment-Request-Id', paymentChallenge.paymentRequestId);
+      }
       const retryInit: RequestInit = { ...originalRequest.init, headers: retryHeaders };
 
       logger.info('X402: retrying request with X-PAYMENT header');
diff --git a/packages/atxp-express/src/atxpExpress.ts b/packages/atxp-express/src/atxpExpress.ts
index 7259b91..3f683eb 100644
--- a/packages/atxp-express/src/atxpExpress.ts
+++ b/packages/atxp-express/src/atxpExpress.ts
@@ -13,6 +13,7 @@ import {
   sendOAuthMetadataNode,
   detectProtocol,
   getPendingPaymentChallenge,
+  setPaymentRequestId,
   type PaymentProtocol,
   type ATXPConfig,
   type TokenCheck,
@@ -51,6 +52,7 @@ export function atxpExpress(args: ATXPArgs): Router {
       // with full pricing context (amount, options, destination).
       const detected = detectProtocol({
         'x-atxp-payment': req.headers['x-atxp-payment'] as string | undefined,
+        'x-atxp-payment-request-id': req.headers['x-atxp-payment-request-id'] as string | undefined,
         'payment-signature': req.headers['payment-signature'] as string | undefined,
         'x-payment': req.headers['x-payment'] as string | undefined,
         'authorization': req.headers['authorization'] as string | undefined,
@@ -134,9 +136,13 @@ export function atxpExpress(args: ATXPArgs): Router {
           // as paymentRequirements instead of regenerating from server config.
           // For MPP/ATXP: credentials are self-contained, no extra context needed.
           const context: Record<string, unknown> = {
+            ...(detected.paymentRequestId && { paymentRequestId: detected.paymentRequestId }),
             ...(sourceAccountId && { sourceAccountId }),
             destinationAccountId,
           };
+          if (detected.paymentRequestId) {
+            setPaymentRequestId(detected.paymentRequestId);
+          }
 
           if (detected.protocol === 'x402') {
             const parsed = parseCredentialBase64(detected.credential);
diff --git a/packages/atxp-server/src/atxpContext.ts b/packages/atxp-server/src/atxpContext.ts
index 5442e61..2b99311 100644
--- a/packages/atxp-server/src/atxpContext.ts
+++ b/packages/atxp-server/src/atxpContext.ts
@@ -13,6 +13,8 @@ export type DetectedCredential = {
   credential: string;
   /** User identity resolved from OAuth token or credential source */
   sourceAccountId?: string;
+  /** Payment request id carried from the 402 challenge retry, when available. */
+  paymentRequestId?: string;
 };
 
 /**
@@ -33,6 +35,8 @@ type ATXPContext = {
   resource: URL;
   /** Payment credential from retry request (X-PAYMENT, X-ATXP-PAYMENT, etc.) */
   detectedCredential?: DetectedCredential;
+  /** Stable lifecycle id for the current paid retry, shared by settle and charge. */
+  paymentRequestId?: string;
   /** Payment challenge pending response rewrite (set by omniChallengeMcpError) */
   pendingPaymentChallenge?: PendingPaymentChallenge;
 }
@@ -75,6 +79,21 @@ export function setDetectedCredential(credential: DetectedCredential): void {
   const context = contextStorage.getStore();
   if (context) {
     context.detectedCredential = credential;
+    if (credential.paymentRequestId) {
+      context.paymentRequestId = credential.paymentRequestId;
+    }
+  }
+}
+
+export function getPaymentRequestId(): string | null {
+  const context = contextStorage.getStore();
+  return context?.paymentRequestId ?? null;
+}
+
+export function setPaymentRequestId(paymentRequestId: string): void {
+  const context = contextStorage.getStore();
+  if (context) {
+    context.paymentRequestId = paymentRequestId;
   }
 }
 
diff --git a/packages/atxp-server/src/index.ts b/packages/atxp-server/src/index.ts
index 0a7cdd2..d646f81 100644
--- a/packages/atxp-server/src/index.ts
+++ b/packages/atxp-server/src/index.ts
@@ -24,6 +24,8 @@ export {
   getATXPResource,
   atxpAccountId,
   atxpToken,
+  getPaymentRequestId,
+  setPaymentRequestId,
   withATXPContext,
   getDetectedCredential,
   setDetectedCredential,
@@ -124,4 +126,3 @@ export {
 export {
   ATXPAccount
 } from '@atxp/common';
-
diff --git a/packages/atxp-server/src/protocol.test.ts b/packages/atxp-server/src/protocol.test.ts
index 37ef919..f5b114f 100644
--- a/packages/atxp-server/src/protocol.test.ts
+++ b/packages/atxp-server/src/protocol.test.ts
@@ -12,6 +12,19 @@ describe('detectProtocol', () => {
     });
   });
 
+  it('should carry payment request id from the retry header', () => {
+    const result = detectProtocol({
+      'x-payment': 'some-x402-payment-credential',
+      'x-atxp-payment-request-id': 'pr_123',
+    });
+
+    expect(result).toEqual({
+      protocol: 'x402',
+      credential: 'some-x402-payment-credential',
+      paymentRequestId: 'pr_123',
+    });
+  });
+
   it('should NOT detect Bearer JWT as ATXP (could be OAuth token)', () => {
     const jwt = 'eyJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJ0ZXN0In0.signature123';
     const result = detectProtocol({
@@ -267,10 +280,14 @@ describe('ProtocolSettlement', () => {
         source: 'did:pkh:eip155:4217:0xSrc',
       };
       const credential = Buffer.from(JSON.stringify(mppCredential)).toString('base64');
-      await settlement.settle('mpp', credential, { sourceAccountId: 'tempo:0xTestUser' });
+      await settlement.settle('mpp', credential, {
+        sourceAccountId: 'tempo:0xTestUser',
+        paymentRequestId: 'pr_mpp_1',
+      });
 
       const body = JSON.parse(mockFetch.mock.calls[0][1].body);
       expect(body.sourceAccountId).toBe('tempo:0xTestUser');
+      expect(body.paymentRequestId).toBe('pr_mpp_1');
     });
 
     it('should include sourceAccountId in X402 settle when context provides it', async () => {
@@ -284,10 +301,12 @@ describe('ProtocolSettlement', () => {
       await settlement.settle('x402', credential, {
         paymentRequirements: { network: 'base' },
         sourceAccountId: 'base:0xTestUser',
+        paymentRequestId: 'pr_x402_1',
       });
 
       const body = JSON.parse(mockFetch.mock.calls[0][1].body);
       expect(body.sourceAccountId).toBe('base:0xTestUser');
+      expect(body.paymentRequestId).toBe('pr_x402_1');
     });
 
     it('should handle raw JSON MPP credential (not base64)', async () => {
diff --git a/packages/atxp-server/src/protocol.ts b/packages/atxp-server/src/protocol.ts
index 9719059..758f2b1 100644
--- a/packages/atxp-server/src/protocol.ts
+++ b/packages/atxp-server/src/protocol.ts
@@ -41,6 +41,7 @@ export type MppChallengeData = {
 export type CredentialDetection = {
   protocol: PaymentProtocol;
   credential: string;
+  paymentRequestId?: string;
 };
 
 /**
@@ -92,6 +93,8 @@ export type OmniChallenge = {
 export type SettlementContext = {
   /** X402: the original payment requirements from the challenge */
   paymentRequirements?: unknown;
+  /** Stable id tying settlement and the follow-up charge to one payment lifecycle. */
+  paymentRequestId?: string;
   /** Source account identifier (e.g., "base:0xABC..." from OAuth sub or wallet address).
    *  When present, auth records the payment for this identity. */
   sourceAccountId?: string;
@@ -134,26 +137,29 @@ export type SettleResult = {
  */
 export function detectProtocol(headers: {
   'x-atxp-payment'?: string;
+  'x-atxp-payment-request-id'?: string;
   'payment-signature'?: string;
   'x-payment'?: string;
   'authorization'?: string;
 }): CredentialDetection | null {
+  const paymentRequestId = headers['x-atxp-payment-request-id'];
+
   // X-ATXP-PAYMENT header indicates ATXP protocol (pull mode credential)
   const atxpPayment = headers['x-atxp-payment'];
   if (atxpPayment) {
-    return { protocol: 'atxp', credential: atxpPayment };
+    return { protocol: 'atxp', credential: atxpPayment, ...(paymentRequestId && { paymentRequestId }) };
   }
 
   // PAYMENT-SIGNATURE (v2) or X-PAYMENT (v1) header indicates X402 protocol
   const paymentSig = headers['payment-signature'] || headers['x-payment'];
   if (paymentSig) {
-    return { protocol: 'x402', credential: paymentSig };
+    return { protocol: 'x402', credential: paymentSig, ...(paymentRequestId && { paymentRequestId }) };
   }
 
   // Authorization: Payment <credential> indicates standard MPP protocol
   const authHeader = headers['authorization'];
   if (authHeader?.startsWith('Payment ')) {
-    return { protocol: 'mpp', credential: authHeader.slice('Payment '.length) };
+    return { protocol: 'mpp', credential: authHeader.slice('Payment '.length), ...(paymentRequestId && { paymentRequestId }) };
   }
 
   return null;
@@ -347,6 +353,7 @@ export class ProtocolSettlement {
       return {
         payload,
         paymentRequirements: requirements,
+        ...(context?.paymentRequestId && { paymentRequestId: context.paymentRequestId }),
         ...(context?.sourceAccountId && { sourceAccountId: context.sourceAccountId }),
         ...(this.destinationAccountId && { destinationAccountId: this.destinationAccountId }),
       };
@@ -362,6 +369,7 @@ export class ProtocolSettlement {
       }
       return {
         credential: parsedCredential,
+        ...(context?.paymentRequestId && { paymentRequestId: context.paymentRequestId }),
         ...(context?.sourceAccountId && { sourceAccountId: context.sourceAccountId }),
         ...(this.destinationAccountId && { destinationAccountId: this.destinationAccountId }),
       };
@@ -388,6 +396,7 @@ export class ProtocolSettlement {
       destinationAccountId: this.destinationAccountId ?? context?.destinationAccountId,
       sourceAccountToken: parsed.sourceAccountToken ?? credential,
       options,
+      ...(context?.paymentRequestId && { paymentRequestId: context.paymentRequestId }),
     };
   }
 }
diff --git a/packages/atxp-server/src/requirePayment.ts b/packages/atxp-server/src/requirePayment.ts
index 93809fc..dda3277 100644
--- a/packages/atxp-server/src/requirePayment.ts
+++ b/packages/atxp-server/src/requirePayment.ts
@@ -1,6 +1,6 @@
 import { RequirePaymentConfig, extractNetworkFromAccountId, extractAddressFromAccountId, Network, AuthorizationServerUrl } from "@atxp/common";
 import { BigNumber } from "bignumber.js";
-import { getATXPConfig, atxpAccountId, atxpToken, setPendingPaymentChallenge } from "./atxpContext.js";
+import { getATXPConfig, atxpAccountId, atxpToken, getPaymentRequestId, setPendingPaymentChallenge } from "./atxpContext.js";
 import { buildPaymentOptions, omniChallengeMcpError } from "./omniChallenge.js";
 import { getATXPResource } from "./atxpContext.js";
 import { signOpaqueIdentity } from "./opaqueIdentity.js";
@@ -28,6 +28,7 @@ export async function requirePayment(paymentConfig: RequirePaymentConfig): Promi
 
   // Get the user's token for on-demand charging (connection_token flow)
   const token = atxpToken();
+  const paymentRequestId = getPaymentRequestId();
 
   // Always use multi-option format
   const charge = {
@@ -41,6 +42,7 @@ export async function requirePayment(paymentConfig: RequirePaymentConfig): Promi
     destinationAccountId: destinationAccountId,
     payeeName: config.payeeName,
     ...(token && { sourceAccountToken: token }),
+    ...(paymentRequestId && { paymentRequestId }),
   };
 
   // Settlement is handled by the middleware (atxpExpress) before route code runs.
diff --git a/packages/atxp-server/src/types.ts b/packages/atxp-server/src/types.ts
index 6369641..c6d7ddb 100644
--- a/packages/atxp-server/src/types.ts
+++ b/packages/atxp-server/src/types.ts
@@ -43,6 +43,8 @@ export type RefundErrors = boolean | 'nonMcpOnly';
 export type Charge = Pick<PaymentRequest, 'options' | 'sourceAccountId' | 'destinationAccountId' | 'payeeName'> & {
   // User's OAuth token or connection_token for on-demand charging
   sourceAccountToken?: string;
+  /** Stable id tying /settle/* and the follow-up /charge to one user-visible payment. */
+  paymentRequestId?: string;
 };
 
 export type BalanceRequest = {