diff --git a/common/api.js b/common/api.js
index 46ed467..febdb3d 100644
--- a/common/api.js
+++ b/common/api.js
@@ -113,9 +113,7 @@ var default_api = 'https://api.global-interaction.com/';
             );
             if (payloadUserID) return payloadUserID;
 
-            var textUserID = firstLongNumericID(
-                decodeBase64URLText(parts[i])
-            );
+            var textUserID = firstLongNumericID(decodeBase64URLText(parts[i]));
             if (textUserID) return textUserID;
         }
         return '';
@@ -254,6 +252,16 @@ var default_api = 'https://api.global-interaction.com/';
         return appCode === 'yumi' || appCode === 'aslan' ? appCode : 'lalu';
     }
 
+    function backendAppCode(appCode) {
+        appCode = String(appCode || 'lalu')
+            .trim()
+            .toLowerCase();
+        // H5 的 app_code 同时承载历史品牌主题和后端租户；yumi/aslan 只用于页面主题，后端当前只有 lalu/huwaa 租户。
+        // 请求头必须收敛到后端已注册的 app_code，否则 gateway 会在 AppRegistryService.ResolveApp 阶段直接返回 INVALID_ARGUMENT。
+        if (appCode === 'yumi' || appCode === 'aslan') return 'lalu';
+        return appCode || 'lalu';
+    }
+
     function applyAppTheme(appCode) {
         if (!window.document || !window.document.documentElement) return;
         window.document.documentElement.setAttribute(
@@ -446,9 +454,10 @@ var default_api = 'https://api.global-interaction.com/';
         );
         var token = getAccessToken();
         var appCode = getAppCode();
+        var requestAppCode = backendAppCode(appCode);
         var url = buildURL(path, opts.query);
         if (token) headers.Authorization = 'Bearer ' + token;
-        if (appCode) headers['X-App-Code'] = appCode;
+        if (requestAppCode) headers['X-App-Code'] = requestAppCode;
         if (!shouldPersist() && isSameOriginURL(url))
             headers['Cache-Control'] = 'no-cache';