Looks like all it needed was the closing ?>, so:
<?php
add_action( 'widgets_init', 'startup_widgets_init_child' );
function startup_widgets_init_child() {
register_sidebar( array (
'name' => __('Footer Widget Area 2', 'startup' ),
'id' => 'footer-widget-area-2',
'before_widget' => '<li id="%1$s" class="widget-container %2$s">',
'after_widget' => "</li>",
'before_title' => '<h3 class="widget-title">',
'after_title' => '</h3>',
) );
}
?>Here’s a full working example:
https://startupwp.com/downloads/support/startuppro-child%28adding-new-widget-area%29.zip
Remember, since you already have a child theme installed, you cannot simply install this new one. Make sure to combine all your child theme customizations into one child theme and upload via FTP.