diff --git a/api/apps/llm_app.py b/api/apps/llm_app.py
index 19fbbece2..d7a852b0b 100644
--- a/api/apps/llm_app.py
+++ b/api/apps/llm_app.py
@@ -130,8 +130,7 @@ def add_llm():
         # For VolcEngine, due to its special authentication method
         # Assemble ark_api_key endpoint_id into api_key
         llm_name = req["llm_name"]
-        api_key = '{' + f'"ark_api_key": "{req.get("ark_api_key", "")}", ' \
-                        f'"ep_id": "{req.get("endpoint_id", "")}" ' + '}'
+        api_key = f'{{ "ark_api_key":"{req.get("ark_api_key", "")}", "ep_id":"{req.get("endpoint_id", "")}" }}'
     elif factory == "Tencent Hunyuan":
         api_key = '{' + f'"hunyuan_sid": "{req.get("hunyuan_sid", "")}", ' \
                         f'"hunyuan_sk": "{req.get("hunyuan_sk", "")}"' + '}'