免费账户一次也不能回测么？不是说能回测三次吗？

from datetime import date
from tqsdk import TqApi, TqAuth, TqBacktest, BacktestFinished

api = TqApi(backtest=TqBacktest(start_dt=date(2021, 8, 1), end_dt=date(2021, 8, 25)), auth=TqAuth("xxx", "xxx"))

quote = api.get_quote("KQ.m@DCE.p")
print(quote.datetime, quote.underlying_symbol)
try:
    while True:
        api.wait_update()
        if api.is_changing(quote, "underlying_symbol"):
            print(quote.datetime, quote.underlying_symbol)
except BacktestFinished:
    api.close()

api = TqApi(backtest=TqBacktest(start_dt=date(2021, 8, 1), end_dt=date(2021, 8, 25)), auth=TqAuth(“xxx”, “xxx”))
File “C:\Users\blquant\.conda\envs\TF2.1\lib\site-packages\tqsdk\api.py”, line 290, in __init__
if not self.wait_update(deadline=deadline): # 等待连接成功并收取截面数据
File “C:\Users\blquant\.conda\envs\TF2.1\lib\site-packages\tqsdk\api.py”, line 1724, in wait_update
self._run_until_idle()
File “C:\Users\blquant\.conda\envs\TF2.1\lib\site-packages\tqsdk\api.py”, line 3107, in _run_until_idle
self._run_once()
File “C:\Users\blquant\.conda\envs\TF2.1\lib\site-packages\tqsdk\api.py”, line 3100, in _run_once
raise self._exceptions.pop(0)
File “C:\Users\blquant\.conda\envs\TF2.1\lib\site-packages\tqsdk\backtest.py”, line 93, in _run
raise Exception(“您的账户不支持回测功能，需要购买专业版本后使用。升级网址：https://account.shinnytech.com”)
Exception: 您的账户不支持回测功能，需要购买专业版本后使用。升级网址：https://account.shinnytech.com