diff --git a/lib/config.ts b/lib/config.ts
index 68d3075..43682e8 100644
--- a/lib/config.ts
+++ b/lib/config.ts
@@ -76,6 +76,10 @@ type InitConfig = {
   // When true, a 'pageview' event is fired once after passport init with full page context.
   // Implies pageContext: true when no pageContext is explicitly configured.
   initContextual?: boolean;
+  // When enabled, detects 403/404 responses from the Site config call and fires a
+  // best-effort profile() call with { error_403: hostname } or { error_404: hostname }.
+  // Pass true to use the "default-sdk" catch-all source, or { site: "slug" } to override the target source.
+  reportMisconfiguration?: boolean | { site?: string };
 };
 
 type ResolvedConfig = {
@@ -97,6 +101,7 @@ type ResolvedConfig = {
   abTests?: ABTestConfig[];
   additionalTargetingSignals?: TargetingSignals;
   timeout?: string;
+  reportMisconfiguration?: boolean | { site?: string };
 };
 
 const DCN_DEFAULTS = {
@@ -133,6 +138,7 @@ function getConfig(init: InitConfig): ResolvedConfig {
     abTests: init.abTests,
     additionalTargetingSignals: init.additionalTargetingSignals,
     timeout: init.timeout,
+    reportMisconfiguration: init.reportMisconfiguration,
   };
 
   if (init.consent?.static) {
diff --git a/lib/core/network.ts b/lib/core/network.ts
index a6b2aad..3684e37 100644
--- a/lib/core/network.ts
+++ b/lib/core/network.ts
@@ -2,6 +2,15 @@ import type { ResolvedConfig } from "../config";
 import { default as buildInfo } from "../build.json";
 import { LocalStorage } from "./storage";
 
+class FetchError extends Error {
+  status: number;
+  constructor(message: string, status: number) {
+    super(message);
+    this.name = "FetchError";
+    this.status = status;
+  }
+}
+
 function buildRequest(path: string, config: ResolvedConfig, init?: RequestInit): Request {
   const { host, cookies } = config;
 
@@ -74,7 +83,7 @@ async function fetch<T>(path: string, config: ResolvedConfig, init?: RequestInit
   const data = contentType?.startsWith("application/json") ? await response.json() : await response.text();
 
   if (!response.ok) {
-    throw new Error(data.error);
+    throw new FetchError(data?.error ?? response.statusText, response.status);
   }
 
   if (data.passport) {
@@ -92,5 +101,5 @@ async function fetch<T>(path: string, config: ResolvedConfig, init?: RequestInit
   return data;
 }
 
-export { fetch, buildRequest };
+export { fetch, buildRequest, FetchError };
 export default fetch;
diff --git a/lib/sdk.test.ts b/lib/sdk.test.ts
index 5a4153f..73b3955 100644
--- a/lib/sdk.test.ts
+++ b/lib/sdk.test.ts
@@ -3,6 +3,8 @@ import { OptableSDK, normalizeTargetingRequest } from "./sdk";
 import { TEST_BASE_URL, TEST_HOST, TEST_SITE } from "./test/mocks";
 import { DCN_DEFAULTS } from "./config";
 import { waitFor } from "./test/utils";
+import { server } from "./test/server";
+import { http, HttpResponse } from "msw";
 
 const defaultConsent = DCN_DEFAULTS.consent;
 
@@ -603,3 +605,272 @@ describe("normalizeTargetingRequest", () => {
     expect(() => normalizeTargetingRequest(3)).toThrowError(/Expected string or object/);
   });
 });
+
+describe("reportMisconfiguration", () => {
+  beforeEach(() => {
+    localStorage.clear();
+    jest.clearAllMocks();
+  });
+
+  test("when reportMisconfiguration: true and Site() returns 403, profile is called with error_403", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    // Mock 403 response for config endpoint
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Forbidden" }, { status: 403 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: true,
+    });
+
+    await sdk["init"];
+
+    // Should have called profile with error_403 and o=default-sdk
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=default-sdk"),
+          _bodyText: expect.stringContaining('"error_403":"localhost"'),
+        })
+      );
+    });
+  });
+
+  test("when reportMisconfiguration: true and Site() returns 404, profile is called with error_404", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    // Mock 404 response for config endpoint
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Not Found" }, { status: 404 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: true,
+    });
+
+    await sdk["init"];
+
+    // Should have called profile with error_404 and o=default-sdk
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=default-sdk"),
+          _bodyText: expect.stringContaining('"error_404":"localhost"'),
+        })
+      );
+    });
+  });
+
+  test("when reportMisconfiguration: false and Site() returns 403, profile is NOT called", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    // Mock 403 response for config endpoint
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Forbidden" }, { status: 403 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: false,
+    });
+
+    await sdk["init"];
+
+    // Should NOT have called profile
+    expect(fetchSpy).not.toHaveBeenCalledWith(
+      expect.objectContaining({
+        url: expect.stringContaining("profile"),
+      })
+    );
+  });
+
+  test("when reportMisconfiguration not set and Site() returns 403, profile is NOT called", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    // Mock 403 response for config endpoint
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Forbidden" }, { status: 403 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+    });
+
+    await sdk["init"];
+
+    // Should NOT have called profile
+    expect(fetchSpy).not.toHaveBeenCalledWith(
+      expect.objectContaining({
+        url: expect.stringContaining("profile"),
+      })
+    );
+  });
+
+  test("when reportMisconfiguration: true and Site() returns 500, profile is called with error_500", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    // Mock 500 response for config endpoint
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Internal Server Error" }, { status: 500 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: true,
+    });
+
+    await sdk["init"];
+
+    // Should have called profile with error_500 and o=default-sdk
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=default-sdk"),
+          _bodyText: expect.stringContaining('"error_500":"localhost"'),
+        })
+      );
+    });
+  });
+
+  test("when reportMisconfiguration: true and Site() throws TypeError (network error), profile is called with error_config", async () => {
+    // Mock fetch to throw TypeError for config endpoint, but allow profile call through
+    const originalFetch = window.fetch;
+    const fetchSpy = jest.spyOn(window, "fetch").mockImplementation((input: any) => {
+      if (typeof input === "string" && input.includes("/config")) {
+        return Promise.reject(new TypeError("Failed to fetch"));
+      }
+      return originalFetch(input);
+    });
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: true,
+    });
+
+    await sdk["init"];
+
+    // Should have called profile with error_config and o=default-sdk
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=default-sdk"),
+          _bodyText: expect.stringContaining('"error_config":"localhost"'),
+        })
+      );
+    });
+
+    fetchSpy.mockRestore();
+  });
+
+  test("when reportMisconfiguration not set and Site() throws TypeError, profile is NOT called", async () => {
+    // Mock fetch to throw TypeError for config endpoint
+    const originalFetch = window.fetch;
+    const fetchSpy = jest.spyOn(window, "fetch").mockImplementation((input: any) => {
+      if (typeof input === "string" && input.includes("/config")) {
+        return Promise.reject(new TypeError("Failed to fetch"));
+      }
+      return originalFetch(input);
+    });
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+    });
+
+    await sdk["init"];
+
+    // Should NOT have called profile
+    expect(fetchSpy).not.toHaveBeenCalledWith(
+      expect.objectContaining({
+        url: expect.stringContaining("profile"),
+      })
+    );
+
+    fetchSpy.mockRestore();
+  });
+
+  test("when reportMisconfiguration: { site } and Site() returns 403, profile is called with the custom site slug", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Forbidden" }, { status: 403 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: { site: "my-error-source" },
+    });
+
+    await sdk["init"];
+
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=my-error-source"),
+          _bodyText: expect.stringContaining('"error_403":"localhost"'),
+        })
+      );
+    });
+  });
+
+  test("when reportMisconfiguration: {} and Site() returns 403, profile falls back to default-sdk", async () => {
+    const fetchSpy = jest.spyOn(window, "fetch");
+
+    server.use(
+      http.get(`${TEST_BASE_URL}/config`, async ({}) => {
+        return HttpResponse.json({ error: "Forbidden" }, { status: 403 });
+      })
+    );
+
+    const sdk = new OptableSDK({
+      ...defaultConfig,
+      initPassport: true,
+      reportMisconfiguration: {},
+    });
+
+    await sdk["init"];
+
+    await waitFor(() => {
+      expect(fetchSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: "POST",
+          url: expect.stringContaining("profile"),
+          url: expect.stringContaining("o=default-sdk"),
+          _bodyText: expect.stringContaining('"error_403":"localhost"'),
+        })
+      );
+    });
+  });
+});
diff --git a/lib/sdk.ts b/lib/sdk.ts
index 3f4ba40..da22900 100644
--- a/lib/sdk.ts
+++ b/lib/sdk.ts
@@ -24,6 +24,7 @@ import { Profile } from "./edge/profile";
 import { sha256 } from "js-sha256";
 import { Tokenize, TokenizeResponse } from "./edge/tokenize";
 import { LocalStorage } from "./core/storage";
+import { FetchError } from "./core/network";
 
 class OptableSDK {
   public static version = buildInfo.version;
@@ -47,7 +48,15 @@ class OptableSDK {
 
   async initialize(): Promise<void> {
     if (this.dcn.initPassport) {
-      await Site(this.dcn).catch(() => {});
+      await Site(this.dcn).catch((err) => {
+        if (this.dcn.reportMisconfiguration) {
+          const status = err instanceof FetchError ? err.status : null;
+          const key = status ? `error_${status}` : "error_config";
+          const cfg = this.dcn.reportMisconfiguration;
+          const reportSite = typeof cfg === "object" ? (cfg.site ?? "default-sdk") : "default-sdk";
+          Profile({ ...this.dcn, site: reportSite }, { [key]: window.location.hostname }).catch(() => {});
+        }
+      });
     }
 
     if (this.dcn.initTargeting) {