didStartRinging(_ call: DirectCall) Methods doesn't get called

I have an issue in receiving calls in ios.

        let params = AuthenticateParams(userId: "testuser", accessToken: "bb52e2f89cc0b4a56e91bac50d4ed19f3999493f")
        SendBirdCall.authenticate(with: params) { (user, error) in
            guard let user = user, error == nil else { return }

I am using this methods to authenticate user in send bird.

When I put debug breakpoint and at the authenticate’s callback and dial a call then I am able to receive call. I think the user get disconnected after authenticate method.

Please provide solution !