diff --git a/src/errors/codes.ts b/src/errors/codes.ts
index fbbeb6d..7a84f1d 100644
--- a/src/errors/codes.ts
+++ b/src/errors/codes.ts
@@ -244,10 +244,7 @@ export const ErrorCode = {
   UNSUPPORTED_MEDIA_TYPE: "UNSUPPORTED_MEDIA_TYPE",
 
   /** Request is syntactically correct but semantically invalid */
-  UNPROCESSABLE_ENTITY: "UNPROCESSABLE_ENTITY",
-
-  /** Usage aggregate not found for the given developer */
-  USAGE_AGGREGATE_NOT_FOUND: "USAGE_AGGREGATE_NOT_FOUND"
+  UNPROCESSABLE_ENTITY: "UNPROCESSABLE_ENTITY"
 
 } as const;
 
diff --git a/src/routes/admin.ts b/src/routes/admin.ts
index a692bb9..7d591c9 100644
--- a/src/routes/admin.ts
+++ b/src/routes/admin.ts
@@ -15,6 +15,7 @@ import {
 } from '../services/quotaService.js';
 import { createAdminWebhooksRouter } from './admin/webhooks.js';
 import { createAdminApisRouter } from './admin/apis.js';
+import { createMaintenanceBannerRouter } from './admin/maintenance/banner.js';
 
 const TRUST_PROXY = process.env.TRUST_PROXY_HEADERS === 'true';
 const usageStore: UsageAdminStore = createUsageStore();
@@ -211,4 +212,9 @@ router.use('/webhooks', createAdminWebhooksRouter());
 // ---------------------------------------------------------------------------
 router.use('/apis', createAdminApisRouter());
 
+// Admin maintenance banner management
+// Mounts:   POST   /api/admin/maintenance/banner
+// ---------------------------------------------------------------------------
+router.use('/maintenance/banner', createMaintenanceBannerRouter());
+
 export default router;
\ No newline at end of file
diff --git a/src/routes/admin/maintenance/banner.test.ts b/src/routes/admin/maintenance/banner.test.ts
new file mode 100644
index 0000000..a076d11
--- /dev/null
+++ b/src/routes/admin/maintenance/banner.test.ts
@@ -0,0 +1,60 @@
+import express from "express";
+import supertest from "supertest";
+import { createMaintenanceBannerRouter } from "./banner.js";
+
+describe("Admin Maintenance Banner Endpoint", () => {
+  let app: express.Express;
+
+  beforeAll(() => {
+    app = express();
+    app.use(express.json());
+    
+    // Mock administrative auth middleware to inject required res.locals context
+    app.use((req, res, next) => {
+      res.locals.adminActor = { id: "admin_test_user", role: "superadmin" };
+      next();
+    });
+
+    // Mount the sub-router under the exact target path for isolated integration testing
+    app.use("/api/admin/maintenance/banner", createMaintenanceBannerRouter());
+  });
+
+  // ── SUCCESSFUL CASE ──────────────────────────────────────────────────────────
+  it("should successfully set the maintenance banner and return 200", async () => {
+    const response = await supertest(app)
+      .post("/api/admin/maintenance/banner")
+      .send({
+        message: "System upgrade in progress",
+        isActive: true,
+      });
+
+    expect(response.status).toBe(200);
+    expect(response.body).toHaveProperty("data");
+    expect(response.body.data.message).toBe("System upgrade in progress");
+    expect(response.body.data.isActive).toBe(true);
+    expect(response.body.data).toHaveProperty("updatedAt");
+  });
+
+  // ──  (INPUT VALIDATION EDGE CASES) ──────────────────────────────────────
+  it("should return 400 BadRequest if message is missing or empty", async () => {
+    const response = await supertest(app)
+      .post("/api/admin/maintenance/banner")
+      .send({
+        message: "   ",
+        isActive: true,
+      });
+
+    expect(response.status).toBe(400);
+  });
+
+  it("should return 400 BadRequest if isActive is not a boolean", async () => {
+    const response = await supertest(app)
+      .post("/api/admin/maintenance/banner")
+      .send({
+        message: "Valid message",
+        isActive: "true", 
+      });
+
+    expect(response.status).toBe(400);
+  });
+});
\ No newline at end of file
diff --git a/src/routes/admin/maintenance/banner.ts b/src/routes/admin/maintenance/banner.ts
new file mode 100644
index 0000000..3529e5c
--- /dev/null
+++ b/src/routes/admin/maintenance/banner.ts
@@ -0,0 +1,82 @@
+/**
+ * Admin API maintenance banner routes.
+ * * Routes:
+ * POST /api/admin/maintenance/banner — set or update the maintenance banner
+ */
+
+import { Router } from "express";
+import { getClientIp } from "../../../lib/clientIp.js";
+import {
+  BadRequestError,
+  AppError,
+  InternalServerError,
+} from "../../../errors/index.js";
+import { logger } from "../../../logger.js";
+
+const TRUST_PROXY = process.env.TRUST_PROXY_HEADERS === "true";
+
+export interface MaintenanceBannerRouterDeps {
+  
+}
+
+/**
+ * Factory that returns the admin maintenance banner sub-router.
+ */
+export function createMaintenanceBannerRouter(
+  _deps: MaintenanceBannerRouterDeps = {},
+): Router {
+  const router = Router();
+
+  // ── POST /api/admin/maintenance/banner ──────────────────────────────────
+  /**
+   * Set or update the system-wide maintenance banner.
+   * * Returns 200 OK with the updated banner data.
+   */
+  router.post("/", async (req, res, next) => {
+    const { message, isActive } = req.body;
+
+    // 1. Input Validation at the boundary (Criterio de Aceptación)
+    if (typeof message !== "string" || message.trim() === "") {
+      next(new BadRequestError("message must be a non-empty string"));
+      return;
+    }
+
+    if (typeof isActive !== "boolean") {
+      next(new BadRequestError("isActive must be a boolean"));
+      return;
+    }
+
+    try {
+      const correlationId = req.headers["x-request-id"] ?? req.headers["x-correlation-id"];
+      
+      
+      const bannerData = {
+        message: message.trim(),
+        isActive,
+        updatedAt: new Date().toISOString()
+      };
+
+      // 2. Structured logging with correlation IDs (Guideline requerida)
+      logger.audit("SET_MAINTENANCE_BANNER", res.locals.adminActor, {
+        clientIp: getClientIp(req, TRUST_PROXY),
+        userAgent: req.get("User-Agent"),
+        correlationId,
+        diff: bannerData,
+      });
+
+      // 3. Standardized error envelope/response
+      res.status(200).json({ data: bannerData });
+    } catch (error) {
+      if (error instanceof AppError) {
+        next(error);
+        return;
+      }
+      logger.error("Failed to set maintenance banner", { error });
+      next(new InternalServerError());
+    }
+  });
+
+  return router;
+}
+
+export default createMaintenanceBannerRouter;
\ No newline at end of file