getRotorState Error

[KIYONG-KWON]

// Setting.json
{
"SeeDocsAt": "https://github.com/Microsoft/AirSim/blob/master/docs/settings.md",
"SettingsVersion": 1.5,
"SimMode": "Multirotor",

"Vehicles": {
"Drone1": {
"VehicleType": "SimpleFlight",
"X": 4,
"Y": 0,
"Z": -2,
"Yaw": -180
},
"Drone2": {
"VehicleType": "SimpleFlight",
"X": 8,
"Y": 0,
"Z": 0,
"Yaw": -180
}
}
}

// main.cpp
string droneID = "Drone1";
client.enableApiControl(true, droneID);
client.getRotorStates(droneID); // error on this line , rpc::rpc_error

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Cound you advise me why error occurred at this line? other codes to get sensor datas such as gps, imu etc do not make error like this.
I updated Airsim version as the lastest 1.5.0 and unreal version is 4.26.