package com.reactnativenavigation.react;

public class Constants {
    public static final String BACK_BUTTON_JS_KEY = "backButton";
    public static final String BACK_BUTTON_ID = "RNN.back";
    public static final String STATUS_BAR_HEIGHT_KEY = "statusBarHeight";
}

package com.reactnativenavigation.react;

public class Constants {
    public static final String BACK_BUTTON_JS_KEY = "backButtonId";
    public static final String BACK_BUTTON_ID = "RNN.back";
    public static final String STATUS_BAR_HEIGHT_KEY = "statusBarHeight";
}

Rename backButton id constant to backButtonId