MTU change following example

I'm writing an Android application that is using RxAndroidBle, to support my device I need a higher MTU

I followed the provided library example:https://github.com/Polidea/RxAndroidBle/wiki/Tutorial:-MTU-negotiation

But it is not compiling

private ObservableTransformer<RxBleConnection, RxBleConnection> mtuNegotiationObservableTransformer = upstream -> {
        return upstream.doOnSubscribe(ignoredDisposable -> Log.i("MTU", "MTU negotiation is supported")
                     .flatMapSingle(connection ->
                                connection.requestMtu(GATT_MTU_MAXIMUM)
                                        .doOnSubscribe(ignoredDisposable -> Log.i("MTU", "Negotiating MTU started"))
                                        .doOnSuccess(mtu -> Log.i("MTU", "Negotiated MTU: " + mtu))
                                        .ignoreElement()
                                        .andThen(Single.just(connection)));
    };

The compiler message is: cannot resolve method 'flatmapsingle'

Why is it that it is not working? In other parts of my code I´m using .flatMapSingle without a problem. Thanks for helping!

There seem to be a mistake in number of closing brackets. Try the below code:

private ObservableTransformer<RxBleConnection, RxBleConnection> mtuNegotiationObservableTransformer = upstream -> {
    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {
        return upstream.doOnSubscribe(ignoredDisposable -> Log.i("MTU", "MTU negotiation is not supported")); // added a closing bracket here
    }

    return upstream
            .doOnSubscribe(ignoredDisposable -> Log.i("MTU", "MTU negotiation is supported")) // and here
                    .flatMapSingle(connection ->
                            connection.requestMtu(GATT_MTU_MAXIMUM)
                                    .doOnSubscribe(ignoredDisposable -> Log.i("MTU", "Negotiating MTU started"))
                                    .doOnSuccess(mtu -> Log.i("MTU", "Negotiated MTU: " + mtu))
                                    .ignoreElement()
                                    .andThen(Single.just(connection)));
};