diff --git a/src/promptflow-evals/promptflow/evals/synthetic/_model_tools/_proxy_completion_model.py b/src/promptflow-evals/promptflow/evals/synthetic/_model_tools/_proxy_completion_model.py
index 4cee480f996..2fe23e351e6 100644
--- a/src/promptflow-evals/promptflow/evals/synthetic/_model_tools/_proxy_completion_model.py
+++ b/src/promptflow-evals/promptflow/evals/synthetic/_model_tools/_proxy_completion_model.py
@@ -3,6 +3,7 @@
 # ---------------------------------------------------------
 import asyncio
 import copy
+import json
 import logging
 import time
 import uuid
@@ -14,6 +15,22 @@
 from .models import AsyncHTTPClientWithRetry, OpenAIChatCompletionsModel
 
 
+class SimulationRequestDTO:
+    def __init__(self, url, headers, payload, params, templatekey, template_parameters):
+        self.url = url
+        self.headers = headers
+        self.json = json.dumps(payload)
+        self.params = params
+        self.templatekey = templatekey
+        self.templateParameters = template_parameters
+
+    def to_dict(self):
+        return self.__dict__
+
+    def to_json(self):
+        return json.dumps(self.__dict__)
+
+
 class ProxyChatCompletionsModel(OpenAIChatCompletionsModel):
     def __init__(self, name, template_key, template_parameters, *args, **kwargs):
         self.tkey = template_key
@@ -80,7 +97,7 @@ async def request_api(
 
         self._log_request(request_data)
 
-        token = await self.token_manager.get_token()
+        token = self.token_manager.get_token()
 
         proxy_headers = {
             "Authorization": f"Bearer {token}",
@@ -99,19 +116,21 @@ async def request_api(
         if self.api_version:
             params["api-version"] = self.api_version
 
-        sim_request_dict = {
-            "url": self.endpoint_url,
-            "headers": headers,
-            "payload": request_data,
-            "params": params,
-            "templatekey": self.tkey,
-            "template_parameters": self.tparam,
-        }
+        sim_request_dto = SimulationRequestDTO(
+            url=self.endpoint_url,
+            headers=headers,
+            payload=request_data,
+            params=params,
+            templatekey=self.tkey,
+            template_parameters=self.tparam,
+        )
 
         time_start = time.time()
         full_response = None
 
-        async with session.post(url=self.endpoint_url, headers=proxy_headers, json=sim_request_dict) as response:
+        async with session.post(
+            url=self.endpoint_url, headers=proxy_headers, json=sim_request_dto.to_dict()
+        ) as response:
             if response.status == 202:
                 response = await response.json()
                 self.result_url = response["location"]