我执行了以下代码进行模拟交易，为何交易不成功呢？

from tqsdk import TqApi, TqSim
api = TqApi(TqSim(init_balance=100000))

quote = api.get_quote("SHFE.rb1901")
print("Last Price: %f" % (quote.last_price))
print("Bid Price 1: %f" % (quote.bid_price1))
print("Ask Price 1: %f" % (quote.ask_price1))
print("Bid Volume 1: %f" % (quote.bid_volume1))
print("Ask Volume 1: %f" % (quote.ask_volume1))

order = api.insert_order(symbol="SHFE.rb1901", direction="BUY", offset="OPEN", limit_price=quote.ask_price1,volume=2)
print(order)

while order.status != "FINISHED":
  api.wait_update()
  print("委托单状态: %s, 未成交手数: %d 手" % (order.status, order.volume_left))

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