diff --git a/script.js b/script.js
index e414310..8dcd18d 100644
--- a/script.js
+++ b/script.js
@@ -446,10 +446,12 @@
   function getAuthConfig() {
     const cfg = globalThis.AUTH_CONFIG && typeof globalThis.AUTH_CONFIG === "object" ? globalThis.AUTH_CONFIG : {};
     const allowEndUserConfig = Boolean(cfg.allowEndUserConfig);
+    const apiBase = String(cfg.apiBase || "").trim(); // optional, e.g. https://api.ncue.net
     const auth0 = cfg.auth0 && typeof cfg.auth0 === "object" ? cfg.auth0 : {};
     const allowedEmails = Array.isArray(cfg.allowedEmails) ? cfg.allowedEmails : [];
     const base = {
       allowEndUserConfig,
+      apiBase,
       auth0: {
         domain: String(auth0.domain || "").trim(),
         clientId: String(auth0.clientId || "").trim(),
@@ -466,6 +468,7 @@
     // override가 있으면 우선 적용 (서버 재배포 없이 테스트 가능)
     return {
       allowEndUserConfig,
+      apiBase,
       auth0: {
         domain: override.auth0.domain || base.auth0.domain,
         clientId: override.auth0.clientId || base.auth0.clientId,
@@ -479,6 +482,17 @@
     };
   }
 
+  function apiUrl(pathname) {
+    const cfg = getAuthConfig();
+    const base = cfg.apiBase;
+    if (!base) return pathname; // same-origin
+    try {
+      return new URL(pathname, base).toString();
+    } catch {
+      return pathname;
+    }
+  }
+
   function currentUrlNoQuery() {
     // Auth0 callback 후 URL 정리용
     const u = new URL(location.href);
@@ -649,7 +663,7 @@
   async function syncUserToServerWithIdToken(idToken) {
     try {
       const cfg = getAuthConfig();
-      const r = await fetch("/api/auth/sync", {
+      const r = await fetch(apiUrl("/api/auth/sync"), {
         method: "POST",
         headers: {
           Authorization: `Bearer ${idToken}`,
@@ -657,11 +671,18 @@
           "X-Auth0-ClientId": cfg.auth0.clientId,
         },
       });
-      if (!r.ok) return null;
+      if (!r.ok) {
+        toastOnce(
+          "syncfail",
+          `사용자 저장(API)이 실패했습니다. (${r.status}) 정적 호스팅이면 /api 를 서버로 프록시하거나 apiBase를 설정해야 합니다.`
+        );
+        return null;
+      }
       const data = await r.json();
       if (data && data.ok) return Boolean(data.canManage);
       return null;
     } catch {
+      toastOnce("syncerr", "사용자 저장(API)에 연결하지 못했습니다. /api 서버 연결을 확인하세요.");
       return null;
     }
   }
@@ -673,14 +694,14 @@
     // Prefer sendBeacon to survive navigation
     try {
       const blob = new Blob([payload], { type: "application/json" });
-      const ok = navigator.sendBeacon("/api/auth/logout", blob);
+      const ok = navigator.sendBeacon(apiUrl("/api/auth/logout"), blob);
       if (ok) return;
     } catch {
       // ignore
     }
     // Fallback fetch keepalive (best-effort)
     try {
-      fetch("/api/auth/logout", {
+      fetch(apiUrl("/api/auth/logout"), {
         method: "POST",
         headers: {
           Authorization: `Bearer ${idToken}`,