diff --git a/docs/API_REFERENCE.md b/docs/API_REFERENCE.md
index 4c5c932..a84dcb7 100644
--- a/docs/API_REFERENCE.md
+++ b/docs/API_REFERENCE.md
@@ -6,7 +6,7 @@ The live, authoritative reference is generated from the same Zod schemas that va
 
 - All routes are versioned under `/api/v1` except `/health*` and `/api-docs`.
 - Success responses: `{ "data": ..., "meta"?: {...} }`.
-- Error responses: `{ "error": { "code": "...", "message": "...", "details"?: ... } }` — see `src/shared/errors` for the full code list.
+- Error responses: `{ "error": { "code": "...", "message": "...", "details"?: ... }, "requestId": "<fastify request id>" }` — see `src/shared/errors` for the full code list. The top-level `requestId` lets a user reporting a 500 be correlated to the matching `req.id` in the server's request log line.
 - Mutating endpoints that reflect on-chain state (deliveries, escrow, disputes, fleet) return a **pending transaction record**, not a synchronously-updated resource — the underlying resource only reaches its new state once the blockchain indexer confirms the corresponding on-chain event. See `ARCHITECTURE.md` §9.
 - Endpoints that require a wallet-owned signature (`sender`, `recipient`, `driver`, `fleet owner` actions per `PHASE_1_DOMAIN_ANALYSIS.md`) live under `/transactions/build/*` and return unsigned XDR — this backend never signs on a user's behalf (`AUTHENTICATION.md`).
 
diff --git a/src/shared/errors/error-handler.spec.ts b/src/shared/errors/error-handler.spec.ts
index f9d6ad9..1cf1fcf 100644
--- a/src/shared/errors/error-handler.spec.ts
+++ b/src/shared/errors/error-handler.spec.ts
@@ -4,20 +4,26 @@ import { handleError } from './error-handler.js';
 import { AppError } from './app-error.js';
 
 class BlockchainError extends AppError {
+  readonly statusCode = 502;
+  readonly code = 'BLOCKCHAIN_ERROR';
   constructor(message: string, details?: unknown) {
-    super('BLOCKCHAIN_ERROR', message, 502, details);
+    super(message, details);
   }
 }
 
 class InternalError extends AppError {
+  readonly statusCode = 500;
+  readonly code = 'INTERNAL_ERROR';
   constructor(message: string, details?: unknown) {
-    super('INTERNAL_ERROR', message, 500, details);
+    super(message, details);
   }
 }
 
 class ClientError extends AppError {
+  readonly statusCode = 400;
+  readonly code = 'BAD_REQUEST';
   constructor(message: string, details?: unknown) {
-    super('BAD_REQUEST', message, 400, details);
+    super(message, details);
   }
 }
 
@@ -32,6 +38,7 @@ describe('error-handler', () => {
 
   function createMockRequest(logFn: (level: string, arg: unknown, msg: string) => void): FastifyRequest {
     const mockRequest = {
+      id: 'req-123',
       log: {
         error: (arg: unknown, msg: string) => logFn('error', arg, msg),
         warn: (arg: unknown, msg: string) => logFn('warn', arg, msg),
@@ -60,6 +67,7 @@ describe('error-handler', () => {
     expect(sendArg.error.message).toBe('Soroban RPC call failed');
     expect(sendArg.error.code).toBe('BLOCKCHAIN_ERROR');
     expect(sendArg.error.details).toBeUndefined();
+    expect(sendArg.requestId).toBe('req-123');
 
     expect(logs.length).toBeGreaterThan(0);
     const errorLog = logs.find((log) => log.level === 'error');
@@ -151,5 +159,18 @@ describe('error-handler', () => {
     const sendArg = (reply.send as any).mock.calls[0]?.[0];
     expect(sendArg.error.message).toBe('An unexpected error occurred');
     expect(sendArg.error.code).toBe('INTERNAL_ERROR');
+    expect(sendArg.requestId).toBe('req-123');
+  });
+
+  it('includes the request id on 4xx validation responses', () => {
+    const reply = createMockReply();
+    const request = createMockRequest(() => {});
+
+    const error = new ClientError('Bad request', {});
+
+    handleError(error, request, reply);
+
+    const sendArg = (reply.send as any).mock.calls[0]?.[0];
+    expect(sendArg.requestId).toBe('req-123');
   });
 });
diff --git a/src/shared/errors/error-handler.ts b/src/shared/errors/error-handler.ts
index c5e4c62..a891661 100644
--- a/src/shared/errors/error-handler.ts
+++ b/src/shared/errors/error-handler.ts
@@ -8,6 +8,9 @@ interface ErrorResponseBody {
     message: string;
     details?: unknown;
   };
+  /** Fastify request id — appears in the request log line, so a user reporting
+   * an error can share this and support can correlate it to a logged incident. */
+  requestId: string;
 }
 
 /** Duck-typed check — avoids a hard import dependency on @prisma/client's
@@ -39,9 +42,16 @@ export function handleError(
   request: FastifyRequest,
   reply: FastifyReply,
 ): void {
+  const requestId = request.id;
   if (error instanceof AppError) {
+    // 5xx details (e.g. DB connection strings, RPC payloads) are logged
+    // server-side but never echoed back to clients, so they can't leak.
     const body: ErrorResponseBody = {
-      error: { code: error.code, message: error.message, details: error.details },
+      error:
+        error.statusCode >= 500
+          ? { code: error.code, message: error.message }
+          : { code: error.code, message: error.message, details: error.details },
+      requestId,
     };
     if (error.statusCode >= 500) {
       request.log.error({ err: error }, error.message);
@@ -59,6 +69,7 @@ export function handleError(
         message: 'Request validation failed',
         details: zodToDetails(error),
       },
+      requestId,
     };
     void reply.status(400).send(body);
     return;
@@ -78,6 +89,7 @@ export function handleError(
         message: 'Request validation failed',
         details: validationError.validation,
       },
+      requestId,
     };
     void reply.status(400).send(body);
     return;
@@ -87,6 +99,7 @@ export function handleError(
     if (error.code === 'P2002') {
       const body: ErrorResponseBody = {
         error: { code: 'CONFLICT', message: 'Resource already exists', details: error.meta },
+        requestId,
       };
       void reply.status(409).send(body);
       return;
@@ -94,6 +107,7 @@ export function handleError(
     if (error.code === 'P2025') {
       const body: ErrorResponseBody = {
         error: { code: 'NOT_FOUND', message: 'Resource not found' },
+        requestId,
       };
       void reply.status(404).send(body);
       return;
@@ -105,6 +119,7 @@ export function handleError(
           message: 'A related resource required by this operation does not exist',
           details: error.meta,
         },
+        requestId,
       };
       void reply.status(409).send(body);
       return;
@@ -115,6 +130,7 @@ export function handleError(
           code: 'WRITE_CONFLICT',
           message: 'The write conflicted with a concurrent transaction and may be retried',
         },
+        requestId,
       };
       void reply.status(409).send(body);
       return;
@@ -122,6 +138,7 @@ export function handleError(
     if (error.code === 'P1001' || error.code === 'P1002') {
       const body: ErrorResponseBody = {
         error: { code: 'DATABASE_UNAVAILABLE', message: 'The database is currently unreachable' },
+        requestId,
       };
       void reply.status(503).send(body);
       return;
@@ -132,6 +149,7 @@ export function handleError(
   if (typeof fastifyError.statusCode === 'number' && fastifyError.statusCode < 500) {
     const body: ErrorResponseBody = {
       error: { code: fastifyError.code ?? 'BAD_REQUEST', message: fastifyError.message },
+      requestId,
     };
     request.log.warn({ err: error }, error.message);
     void reply.status(fastifyError.statusCode).send(body);
@@ -141,6 +159,7 @@ export function handleError(
   request.log.error({ err: error }, 'Unhandled error');
   const body: ErrorResponseBody = {
     error: { code: 'INTERNAL_ERROR', message: 'An unexpected error occurred' },
+    requestId,
   };
   void reply.status(500).send(body);
 }