diff --git a/packages/atxp-client/package.json b/packages/atxp-client/package.json
index 1025892..69895ba 100644
--- a/packages/atxp-client/package.json
+++ b/packages/atxp-client/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@atxp/client",
-  "version": "0.11.12",
+  "version": "0.11.10",
   "description": "ATXP Client - MCP client with OAuth authentication and payment processing",
   "license": "MIT",
   "repository": {
@@ -33,8 +33,8 @@
     "pack:dry": "npm pack --dry-run"
   },
   "dependencies": {
-    "@atxp/common": "0.11.11",
-    "@atxp/mpp": "0.11.11",
+    "@atxp/common": "0.11.10",
+    "@atxp/mpp": "0.11.10",
     "@modelcontextprotocol/sdk": "^1.15.0",
     "@x402/core": "^2.9.0",
     "@x402/evm": "^2.9.0",
diff --git a/packages/atxp-client/src/atxpAccountHandler.ts b/packages/atxp-client/src/atxpAccountHandler.ts
index 8311ffc..0fada9f 100644
--- a/packages/atxp-client/src/atxpAccountHandler.ts
+++ b/packages/atxp-client/src/atxpAccountHandler.ts
@@ -76,6 +76,7 @@ export class ATXPAccountHandler implements ProtocolHandler {
         paymentRequirements: authorizeParams.paymentRequirements,
         challenge: authorizeParams.challenge,
         challenges: authorizeParams.challenges as unknown[] | undefined,
+        paymentRequestId: typeof challengeData.paymentRequestId === 'string' ? challengeData.paymentRequestId : undefined,
       });
     } catch (error) {
       logger.error(`ATXPAccountHandler: authorize failed: ${error instanceof Error ? error.message : String(error)}`);
diff --git a/packages/atxp-client/src/x402ProtocolHandler.ts b/packages/atxp-client/src/x402ProtocolHandler.ts
index df24e08..4870855 100644
--- a/packages/atxp-client/src/x402ProtocolHandler.ts
+++ b/packages/atxp-client/src/x402ProtocolHandler.ts
@@ -149,6 +149,7 @@ export class X402ProtocolHandler implements ProtocolHandler {
         protocols: ['x402'],
         destination: url,
         paymentRequirements: enrichedRequirements,
+        paymentRequestId: paymentChallenge.paymentRequestId,
       });
       const paymentHeader = authorizeResult.credential;
 
diff --git a/packages/atxp-common/src/atxpAccount.ts b/packages/atxp-common/src/atxpAccount.ts
index ca92299..bcb892e 100644
--- a/packages/atxp-common/src/atxpAccount.ts
+++ b/packages/atxp-common/src/atxpAccount.ts
@@ -339,6 +339,8 @@ export class ATXPAccount implements Account {
     body.currency = 'USDC';
     // X402 fields
     if (params.paymentRequirements) body.paymentRequirements = params.paymentRequirements;
+    // Phase 6: lets accounts key the X402 cap reservation to the challenge so it releases on settle.
+    if (params.paymentRequestId) body.paymentRequestId = params.paymentRequestId;
     // MPP fields
     if (params.challenges) body.challenges = params.challenges;
     if (params.challenge) body.challenge = params.challenge;
diff --git a/packages/atxp-common/src/types.ts b/packages/atxp-common/src/types.ts
index 4ef5767..d007a6f 100644
--- a/packages/atxp-common/src/types.ts
+++ b/packages/atxp-common/src/types.ts
@@ -208,6 +208,11 @@ export interface AuthorizeParams {
   challenge?: unknown;
   /** MPP: array of challenges from multi-chain omni-challenge (preferred) */
   challenges?: unknown[];
+  /**
+   * The challenge's payment-request id. Threaded to accounts at authorize so it can key the
+   * X402 binding cap reservation (upto sessions) to it and release it on settle (Phase 6).
+   */
+  paymentRequestId?: string;
 }
 
 export interface AuthorizeResult {