I have a very strange problem while trying to include a custom file to my child theme. if I try to use get_stylesheet_directory_uri() along with require it crashes the website. if I try to var_dump(get_stylesheet_directory_uri); then shows but PHP errors starts popping up.

Cannot modify header information - headers already sent by - it points the location where I add the require, var_dump. Without it, there are not any errors

Am I not supposed to add a completely new file to the child theme?