Hi @brotsky_pixie
I believe that’s because you were using $post_id variable, which doesn’t have any value yet. Could you please change it to $post->ID instead like this:
echo get_field( "first_name", $post->ID );
To learn more about adding admin custom column, kindly check this page: http://www.elliotcondon.com/advanced-custom-fields-admin-custom-columns/.
I hope this helps 🙂
