Redux callback action

This is an old question but if you are still looking, what you want is the dependency option.

You can use it like this :

Redux::setSection( $opt_name, array(
    'title'  => __( 'Test', 'redux-test' ),
    'id'     => 'switch_buttonset',
    'desc'   => __( '', 'redux-test' ),
    'icon'   => 'el el-cog',
    'fields' => array(
        array(
            'id'      => 'switch-on',
            'type'    => 'switch',
            'title'   => __( 'Switch On', 'redux-framework-demo' ),
            'default' => true,
        ),
        array(
            'id'         => 'opt-text-email',
            'type'       => 'textarea',
            'title'      => __( 'Title', 'redux-test' ),
            'dependency' => array(
                'element' => 'switch-on', //Name of the field that will hide or show this one
                'value'   => array( 'true', 1 ) //The value it should have for it to be displayed
            ),
        )
    )
) );