diff --git a/api/setup_manager.py b/api/setup_manager.py
index a9a01c0..6e420b5 100644
--- a/api/setup_manager.py
+++ b/api/setup_manager.py
@@ -247,6 +247,7 @@ class SetupManager:
             self.config_manager.set_ddns_config(ddns_cfg)
 
             # ── trigger DDNS registration for pic_ngo ─────────────────────────
+            warnings: List[str] = []
             if domain_mode == 'pic_ngo':
                 try:
                     from ddns_manager import DDNSManager
@@ -254,13 +255,29 @@ class SetupManager:
                     ddns_mgr.register(cell_name, '')
                     logger.info(f'DDNS registered: {cell_name}.pic.ngo')
                 except Exception as exc:
-                    logger.warning(f'DDNS registration failed (will retry at next heartbeat): {exc}')
+                    msg = str(exc)
+                    logger.warning(f'DDNS registration failed: {msg}')
+                    if '409' in msg or 'taken' in msg.lower():
+                        warnings.append(
+                            f'The name "{cell_name}" is already registered on pic.ngo. '
+                            'HTTPS will not be active until you re-register: go to '
+                            'Settings → DDNS and click Re-register, or choose a different name.'
+                        )
+                    else:
+                        warnings.append(
+                            'DDNS registration could not be completed right now '
+                            f'({msg}). The cell will retry automatically. '
+                            'HTTPS will activate once registration succeeds.'
+                        )
 
             # ── mark setup complete (must be last) ─────────────────────────
             self.config_manager.set_identity_field('setup_complete', True)
 
             logger.info(f"Setup completed. cell_name={cell_name!r}, domain_mode={domain_mode!r}")
-            return {'success': True, 'redirect': '/login'}
+            result: Dict[str, Any] = {'success': True, 'redirect': '/login'}
+            if warnings:
+                result['warnings'] = warnings
+            return result
 
         finally:
             try:
diff --git a/webui/src/pages/Setup.jsx b/webui/src/pages/Setup.jsx
index 2968b2e..f7734db 100644
--- a/webui/src/pages/Setup.jsx
+++ b/webui/src/pages/Setup.jsx
@@ -540,8 +540,9 @@ function Step4Review({ domainType, domainName, timezone, onBack, onSubmit, submi
 
 export default function Setup() {
   const navigate = useNavigate();
-  const [step, setStep]   = useState(1);
-  const [done, setDone]   = useState(false);
+  const [step, setStep]           = useState(1);
+  const [done, setDone]           = useState(false);
+  const [setupWarnings, setSetupWarnings] = useState([]);
 
   const [password, setPassword]             = useState('');
   const [passwordConfirm, setPasswordConfirm] = useState('');
@@ -600,9 +601,13 @@ export default function Setup() {
     };
 
     try {
-      await setupAPI.complete(payload);
+      const res = await setupAPI.complete(payload);
+      const warnings = res?.data?.warnings || [];
+      setSetupWarnings(warnings);
       setDone(true);
-      setTimeout(() => navigate('/login', { replace: true }), 2000);
+      if (warnings.length === 0) {
+        setTimeout(() => navigate('/login', { replace: true }), 2000);
+      }
     } catch (e) {
       setSubmitError(
         e?.response?.data?.errors?.join(' ') ||
@@ -617,10 +622,27 @@ export default function Setup() {
   if (done) {
     return (
       <div className="flex items-center justify-center min-h-screen bg-gray-950">
-        <div className="text-center">
+        <div className="text-center max-w-md px-4">
           <CheckCircle className="h-12 w-12 text-green-400 mx-auto mb-4" />
           <h2 className="text-lg font-semibold text-white mb-2">Setup complete!</h2>
-          <p className="text-sm text-gray-400">Redirecting to login...</p>
+          {setupWarnings.length > 0 ? (
+            <div className="mt-4 text-left space-y-3">
+              {setupWarnings.map((w, i) => (
+                <div key={i} className="flex gap-2 bg-amber-900/40 border border-amber-700 rounded-lg p-3">
+                  <AlertCircle className="h-4 w-4 text-amber-400 mt-0.5 shrink-0" />
+                  <p className="text-sm text-amber-200">{w}</p>
+                </div>
+              ))}
+              <button
+                onClick={() => navigate('/login', { replace: true })}
+                className="mt-4 w-full py-2 px-4 bg-primary-600 hover:bg-primary-700 text-white rounded-lg text-sm font-medium"
+              >
+                Continue to login
+              </button>
+            </div>
+          ) : (
+            <p className="text-sm text-gray-400">Redirecting to login...</p>
+          )}
         </div>
       </div>
     );