各位老师：
我再IB Paper测试账户订阅行情时出现如下错误，应该如何修正啊？
提前谢过，感谢。

vt_symbols = ['GBP-USD-CASH.IDEALPRO']
#engine.subscribe(vt_symbols)

from vnpy.trader.constant import Exchange
from vnpy.trader.object import SubscribeRequest
req0 = SubscribeRequest(vt_symbols[0],Exchange.IDEALPRO) #创建行情订阅
engine.main_engine.subscribe(req0,"IB")

ticks = engine.get_ticks(vt_symbols)
print(f'Subscribed:\n{ticks}')

Subscribed:
[None]
ERROR 1 321 Error validating request:-'bQ' : cause - Please enter a valid security type
ERROR 2 321 Error validating request:-'bW' : cause - Please enter a valid security type
2020-07-23 02:37:12.945376  信息通知，代码：321，内容: Error validating request:-'bQ' : cause - Please enter a valid security type
2020-07-23 02:37:12.946373  信息通知，代码：321，内容: Error validating request:-'bW' : cause - Please enter a valid security type