diff --git a/ask_gpt.py b/ask_gpt.py
index e94b19a..2c2ce2b 100644
--- a/ask_gpt.py
+++ b/ask_gpt.py
@@ -1,15 +1,9 @@
-"""
-api_endpoint from https://github.com/ayaka14732/ChatGPTAPIFree
-"""
 import aiohttp
 import asyncio
 import json
 
-api_endpoint_free = "https://chatgpt-api.shn.hk/v1/"
-headers = {'Content-Type': "application/json"}
 
-
-async def ask(prompt: str) -> str:
+async def ask(prompt: str, api_endpoint: str, headers: dict) -> str:
     jsons = {
         "model": "gpt-3.5-turbo",
         "messages": [
@@ -20,13 +14,14 @@ async def ask(prompt: str) -> str:
         ],
     }
     async with aiohttp.ClientSession() as session:
-
-        while True:
+        max_try = 5
+        while max_try > 0:
             try:
-                async with session.post(url=api_endpoint_free,
+                async with session.post(url=api_endpoint,
                                         json=jsons, headers=headers, timeout=10) as response:
                     status_code = response.status
                     if not status_code == 200:
+                        max_try = max_try - 1
                         # wait 2s
                         await asyncio.sleep(2)
                         continue
@@ -37,14 +32,3 @@ async def ask(prompt: str) -> str:
             except Exception as e:
                 print(e)
                 pass
-
-
-async def test() -> None:
-    resp = await ask("Hello World")
-    print(resp)
-    # type: str
-    print(type(resp))
-
-
-if __name__ == "__main__":
-    asyncio.run(test())
diff --git a/bot.py b/bot.py
index b14f69b..fe73ddb 100644
--- a/bot.py
+++ b/bot.py
@@ -9,6 +9,14 @@ from ask_gpt import ask
 from send_message import send_room_message
 from v3 import Chatbot
 
+"""
+free api_endpoint from https://github.com/ayaka14732/ChatGPTAPIFree
+"""
+api_endpoint_list = {
+    "free": "https://chatgpt-api.shn.hk/v1/",
+    "paid": "https://api.openai.com/v1/chat/completions"
+}
+
 
 class Bot:
     def __init__(
@@ -37,10 +45,21 @@ class Bot:
         # regular expression to match keyword [!gpt {prompt}] [!chat {prompt}]
         self.gpt_prog = re.compile(r"^\s*!gpt\s*(.+)$")
         self.chat_prog = re.compile(r"^\s*!chat\s*(.+)$")
-        # initialize chatbot
+        # initialize chatbot and api_endpoint
         if self.api_key != '':
             self.chatbot = Chatbot(api_key=self.api_key)
 
+            self.api_endpoint = api_endpoint_list['paid']
+            # request header for !gpt command
+            self.headers = {
+                "Content-Type": "application/json",
+                "Authorization": "Bearer " + self.api_key,
+            }
+        else:
+            self.headers = {
+                "Content-Type": "application/json",
+            }
+
     # message_callback event
     async def message_callback(self, room: MatrixRoom, event: RoomMessageText) -> None:
         # remove newline character from event.body
@@ -55,7 +74,7 @@ class Bot:
             # sending typing state
             await self.client.room_typing(room_id)
             prompt = m.group(1)
-            text = await ask(prompt)
+            text = await ask(prompt, self.api_endpoint, self.headers)
             text = text.strip()
             await send_room_message(self.client, room_id, send_text=text)
 
diff --git a/test.py b/test.py
index 082bd54..825fe3c 100644
--- a/test.py
+++ b/test.py
@@ -4,17 +4,37 @@ from ask_gpt import ask
 import json
 fp = open("config.json", "r")
 config = json.load(fp)
+api_key = config.get('api_key', '')
+api_endpoint_list = {
+    "free": "https://chatgpt-api.shn.hk/v1/",
+    "paid": "https://api.openai.com/v1/chat/completions"
+}
 
 
 def test_v3(prompt: str):
-    bot = Chatbot(api_key=config['api_key'])
+    bot = Chatbot(api_key=api_key)
     resp = bot.ask(prompt=prompt)
     print(resp)
 
 
-async def test_ask(prompt: str):
-    print(await ask(prompt=prompt))
+async def test_ask_gpt_paid(prompt: str):
+    headers = {
+        "Content-Type": "application/json",
+        "Authorization": "Bearer " + api_key,
+    }
+    api_endpoint = api_endpoint_list['paid']
+    # test ask_gpt.py ask()
+    print(await ask(prompt, api_endpoint, headers))
+
+
+async def test_ask_gpt_free(prompt: str):
+    headers = {
+        "Content-Type": "application/json",
+    }
+    api_endpoint = api_endpoint_list['free']
+    print(await ask(prompt, api_endpoint, headers))
 
 if __name__ == "__main__":
     test_v3("Hello World")
-    asyncio.run(test_ask("Hello World"))
+    asyncio.run(test_ask_gpt_paid("Hello World"))
+    asyncio.run(test_ask_gpt_free("Hello World"))