diff --git a/src/services/agent.js b/src/services/agent.js
index ad47bc5..25e918f 100644
--- a/src/services/agent.js
+++ b/src/services/agent.js
@@ -181,17 +181,11 @@ class AgentService {
 
     // Basic policy checks (more complex logic would be here)
     if (amount > fromAgent.policy.spendingLimit) {
-      throw new Error(
-        `Transfer amount exceeds spending limit for agent ${fromAgentId}`,
-      );
+      throw new Error(`Zero Trust Validation Failed: Transfer amount exceeds spending limit for agent ${fromAgentId}`);
     }
-    if (
-      !fromAgent.policy.authorizedCounterparties.includes(toAgentId) &&
-      fromAgent.policy.authorizedCounterparties.length > 0
-    ) {
-      throw new Error(
-        `Agent ${toAgentId} is not an authorized counterparty for ${fromAgentId}`,
-      );
+    if (!fromAgent.policy.authorizedCounterparties.includes(toAgentId) &&
+        fromAgent.policy.authorizedCounterparties.length > 0) {
+      throw new Error(`Zero Trust Validation Failed: Agent ${toAgentId} is not an authorized counterparty for ${fromAgentId}`);
     }
 
     // Simulate transfer success
diff --git a/src/services/mandate.js b/src/services/mandate.js
index dd22396..20feda1 100644
--- a/src/services/mandate.js
+++ b/src/services/mandate.js
@@ -67,27 +67,18 @@ class MandateService {
   }) {
     const decodedIntent = await this.verifyMandate(intentMandate);
 
-    if (decodedIntent.type !== "intent_mandate") {
-      throw new Error(
-        "Zero Trust Validation Failed: Invalid intent mandate type",
-      );
+    if (decodedIntent.type !== 'intent_mandate') {
+      throw new Error('Zero Trust Validation Failed: Invalid intent mandate type');
     }
 
     // Verify budget
     if (totalPrice > decodedIntent.max_budget.value) {
-      throw new Error(
-        "Zero Trust Validation Failed: Cart total exceeds intent mandate budget",
-      );
+      throw new Error('Zero Trust Validation Failed: Cart total exceeds intent mandate budget');
     }
 
     // Verify merchant if whitelist exists
-    if (
-      decodedIntent.allowed_merchants.length > 0 &&
-      !decodedIntent.allowed_merchants.includes(merchantDid)
-    ) {
-      throw new Error(
-        `Zero Trust Validation Failed: Merchant ${merchantDid} is not authorized by this mandate`,
-      );
+    if (decodedIntent.allowed_merchants.length > 0 && !decodedIntent.allowed_merchants.includes(merchantDid)) {
+      throw new Error(`Zero Trust Validation Failed: Merchant ${merchantDid} is not authorized by this mandate`);
     }
 
     // Create cryptographic hash of cart
@@ -120,9 +111,7 @@ class MandateService {
     try {
       return jwt.verify(token, this.signingKey, { algorithms: ["HS256"] });
     } catch (error) {
-      throw new Error(
-        `Zero Trust Validation Failed: Mandate verification failed: ${error.message}`,
-      );
+      throw new Error(`Zero Trust Validation Failed: Mandate verification failed: ${error.message}`);
     }
   }
 
diff --git a/src/services/ucp.js b/src/services/ucp.js
index 918d0b7..2b12df2 100644
--- a/src/services/ucp.js
+++ b/src/services/ucp.js
@@ -42,27 +42,26 @@ class UCPService {
   /**
    * Process a UCP Payload
    * @param {Object} payload - The raw UCP JSON payload
+   * @param {string} mandate - Optional signed Mandate (AP2) for Zero Trust validation
    */
-  async processPayload(payload) {
+  async processPayload(payload, mandate) {
     try {
       // 1. Validate the UCP intent against schema
       const { error, value } = this.ucpIntentSchema.validate(payload, {
         stripUnknown: true,
       });
       if (error) {
-        throw new Error(
-          `Zero Trust Validation Failed: UCP Intent validation failed: ${error.details.map((x) => x.message).join(", ")}`,
-        );
+        throw new Error(`Zero Trust Validation Failed: UCP Intent validation failed: ${error.details.map(x => x.message).join(', ')}`);
       }
 
       const validatedPayload = value;
       const { intent } = validatedPayload;
 
       switch (intent) {
-        case "transfer":
-        case "payment":
-          return this._handleTransfer(validatedPayload);
-        case "purchase":
+        case 'transfer':
+        case 'payment':
+          return this._handleTransfer(validatedPayload, mandate);
+        case 'purchase':
           // Future implementation: integration with Inventory/Order services
           return {
             status: "success",
@@ -85,21 +84,22 @@ class UCPService {
    * Handle transfer/payment intents via A2AService
    * @private
    */
-  async _handleTransfer(payload) {
+  async _handleTransfer(payload, mandate) {
     const { sender, recipient, amount } = payload;
 
     if (!recipient?.agent_id) {
-      throw new Error("Missing recipient agent_id for transfer");
+      throw new Error('Zero Trust Validation Failed: Missing recipient agent_id for transfer');
     }
     if (!amount?.value) {
-      throw new Error("Missing amount value");
+      throw new Error('Zero Trust Validation Failed: Missing amount value');
     }
 
     return this.a2aService.executeTransfer({
       fromAgentId: sender.agent_id,
       toAgentId: recipient.agent_id,
       amount: amount.value,
-      ucpPayload: payload,
+      mandate,
+      ucpPayload: payload
     });
   }
 
diff --git a/tests/unit/mandate_extra.spec.js b/tests/unit/mandate_extra.spec.js
new file mode 100644
index 0000000..322c82b
--- /dev/null
+++ b/tests/unit/mandate_extra.spec.js
@@ -0,0 +1,61 @@
+const MandateService = require('../../src/services/mandate');
+const jwt = require('jsonwebtoken');
+
+describe('MandateService', () => {
+  let mandateService;
+  const signingKey = 'test-secret';
+
+  beforeEach(() => {
+    mandateService = new MandateService({ signingKey });
+  });
+
+  describe('issueCartMandate', () => {
+    it('should throw error for invalid intent mandate type', async () => {
+      const invalidMandate = jwt.sign({ type: 'not_intent' }, signingKey);
+      await expect(mandateService.issueCartMandate({
+        intentMandate: invalidMandate,
+        cartItems: [],
+        totalPrice: 100,
+        merchantDid: 'did:key:m'
+      })).rejects.toThrow('Zero Trust Validation Failed: Invalid intent mandate type');
+    });
+
+    it('should throw error if cart total exceeds budget', async () => {
+      const intentMandate = await mandateService.issueIntentMandate({
+        userDid: 'did:key:u',
+        agentDid: 'did:key:a',
+        maxBudget: 50
+      });
+
+      await expect(mandateService.issueCartMandate({
+        intentMandate,
+        cartItems: [],
+        totalPrice: 100,
+        merchantDid: 'did:key:m'
+      })).rejects.toThrow('Zero Trust Validation Failed: Cart total exceeds intent mandate budget');
+    });
+
+    it('should throw error if merchant is not authorized', async () => {
+      const intentMandate = await mandateService.issueIntentMandate({
+        userDid: 'did:key:u',
+        agentDid: 'did:key:a',
+        maxBudget: 500,
+        allowedMerchants: ['did:key:m1']
+      });
+
+      await expect(mandateService.issueCartMandate({
+        intentMandate,
+        cartItems: [],
+        totalPrice: 100,
+        merchantDid: 'did:key:m2'
+      })).rejects.toThrow('Zero Trust Validation Failed: Merchant did:key:m2 is not authorized by this mandate');
+    });
+  });
+
+  describe('verifyMandate', () => {
+    it('should throw error for invalid token', async () => {
+      await expect(mandateService.verifyMandate('invalid-token'))
+        .rejects.toThrow('Zero Trust Validation Failed: Mandate verification failed: jwt malformed');
+    });
+  });
+});