Connection to Cesium ion failed: can't create connection

When I connect Unreal Engine 5.5.4 with Cesium ion (v2.17), I met the problem as follows: LogCesiumEditor: Error: Failed to obtain ion server application data: Received response code 403
LogCesiumEditor: Error: Error connecting: Failed to obtain _appData, can’t create connection

What should I do? I am in Germany, the network should be fine.