Agora Flutter video call stops after some time with PlatformException(-7, , null, null) - flutter

Question

I am working on a Flutter app that uses a video call feature. I have set up engine initialization and everything correctly and am able to make the video call on both ends successfully. Following is my current version of Agora RTC Engine:
agora_rtc_engine: ^5.3.1
Following is the code I used for engine initialization and initiating video calls.
RtcEngine engine;
var _localUid = 0;
await [Permission.camera, Permission.microphone].request();
engine = await RtcEngine.create(Constants.AGORA_APP_ID);
engine.setEventHandler(
RtcEngineEventHandler(
joinChannelSuccess: (channelId, uid, elapsed) { _localUid = uid; /* my_own_logic */ },
leaveChannel: (RtcStats stats) { /* my_own_logic */ },
userJoined: (int remoteUid, int reason) { /* my_own_logic */ },
userOffline: (remoteUid, reason) { /* my_own_logic */ },
));
await engine.enableVideo();
await engine.enableAudio();
await engine.setVideoEncoderConfiguration(VideoEncoderConfiguration(
dimensions: const VideoDimensions(width: 360, height: 640),
frameRate: VideoFrameRate.Fps60,
bitrate: 0,
));
await engine.setDefaultAudioRouteToSpeakerphone(true);
agoraToken = await fetchAgoraToken(uid: _localUid, channelId: "generatedChannelId");
await engine.setChannelProfile(ChannelProfile.LiveBroadcasting);
await engine.setClientRole(ClientRole.Broadcaster);
await engine.startPreview();
await engine.joinChannel(agoraToken, "generatedChannelId", '', _localUid,);
I'm generating call joining tokens with channel ID, Agora APP ID and Certificate from Firebase Functions and the channel name is always unique between the same two callers.
The video call is working well and I can see/hear other people. But after a few seconds, not more than a minute, the video call stops suddenly. Following is the exact error message I receive on my console
[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: PlatformException(-7, , null, null)
E/flutter (25342): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:653:7)
E/flutter (25342): #1 MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:296:18)
I'm stuck here and unable to work further. Could anybody suggest me how should I fix this?

Answer 1

It turned out that I had earlier placed a timer to schedule cancellation of call if there's no response from the callee. The calling screen was closing after the specified time without leaving channel and destroying the engine, and that was causing the exception.
Timer? callEndTimer;
void scheduleCallEnd() {
callEndTimer = Timer(const Duration(seconds: Constants.INCOMMING_CALL_TIME), () {
if (mounted) {
setState(() {
_onCallEnd(context);
});
}
});
}
Then I cancelled the timer if the call was responded by callee.
void cancelScheduledCallEnd() {
if (callEndTimer != null) callEndTimer!.cancel();
}