AgoraVideoViewController.swift

var agoraRtm: AgoraRtmKit?

override func viewDidLoad() {
    ...
        
    agoraRtm = AgoraRtmKit.init(appId: appID, delegate: self)
}

override func viewWillAppear(_ animated: Bool) {
    handle = Auth.auth().addStateDidChangeListener { (auth, user) in
        self.currentUser = user
        if let user = user {
            self.joinChannel(channelName: user.uid)
            self.agoraRtm?.login(byToken: nil, user: user.displayName ?? user.uid) { (error) in
                if (error != .ok) {
                    print("Failed to login to RTM: ", error.rawValue)
                }
            }
        } else {
            self.agoraRtm?.logout(completion: nil)
            self.showFUIAuthScreen()
        }
    }
}

...

extension AgoraVideoViewController: AgoraRtmDelegate {
    func rtmKit(_ kit: AgoraRtmKit, connectionStateChanged state: AgoraRtmConnectionState, reason: AgoraRtmConnectionChangeReason) {
        if state == .connected {
            chatButton.isEnabled = true
        } else {
            chatButton.isEnabled = false
        }
    }
}