diff --git a/sundynix-gateway/internal/voice/frame.go b/sundynix-gateway/internal/voice/frame.go
index 8e120d1..d9abffc 100644
--- a/sundynix-gateway/internal/voice/frame.go
+++ b/sundynix-gateway/internal/voice/frame.go
@@ -19,6 +19,7 @@ const volcAppKey = "PlgvMymc7f3tQnJ6"
 func setVolcAuthHeaders(hdr http.Header, apiKey, appID, resourceID string) {
 	// 直接赋 map（不走 Set）以**保留精确大小写**：Go 的 Header.Set 会把 "X-Api-App-ID"
 	// 规范化成 "X-Api-App-Id"，而火山网关按精确大小写匹配（官方 demo 用 X-Api-App-ID）。
+	// 新版 API Key 走 X-Api-Access-Key；X-Api-App-Key 是网关固定常量，缺它 400 "app key not found"。
 	hdr["X-Api-App-Key"] = []string{volcAppKey}
 	hdr["X-Api-Access-Key"] = []string{apiKey}
 	hdr["X-Api-Resource-Id"] = []string{resourceID}