XBee-PRO ZB (S2C) TH - InvalidOperatingModeException: Could not determine operating mode #62

from digi.xbee.devices import ZigBeeDevice 
PORT = "/dev/ttyUSB0"  
BAUD_RATE = 9600 
device = ZigBeeDevice(PORT, BAUD_RATE)                                                                                                                                       
device.open()        
                                                                                                                                                        
---------------------------------------------------------------------------
InvalidOperatingModeException             Traceback (most recent call last)
<ipython-input-4-b929a415d2b8> in <module>
----> 1 device.open()

~/py3/lib/python3.6/site-packages/digi/xbee/devices.py in open(self)
   2970            | :meth:`.XBeeDevice.open`
   2971         """
-> 2972         super().open()
   2973         if self.get_protocol() != XBeeProtocol.ZIGBEE:
   2974             raise XBeeException("Invalid protocol.")

~/py3/lib/python3.6/site-packages/digi/xbee/devices.py in open(self)
   1257         if self._operating_mode == OperatingMode.UNKNOWN:
   1258             self.close()
-> 1259             raise InvalidOperatingModeException("Could not determine operating mode")
   1260         if self._operating_mode == OperatingMode.AT_MODE:
   1261             self.close()

InvalidOperatingModeException: Could not determine operating mode