The signature of addActionListener method is public void addActionListener(ActionListener l) where ActionListener it is a functional interface (in Java programming language a functional interface it is an interface with a sole method) defining the actionPerformed method accepting one argument of type ActionEvent, the method signature being void actionPerformed(ActionEvent e).

this::increasePoints it is method reference that should be possible to translate to...

new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        . . .
    }
}

...therefore the increasePoints method signature must match the signature of actionPerformed method defined by th ActionListener interface.