Redirecting a 404 page to another site with the same url?

Question

PHP

Hello.
Moved the site to a new domain.
Hung a new site on the old domain.
Now you need to redirect pages from the old site to the new one, so that the new site on the old domain continues to work.
In general, the meaning is this:
I added the following code to the page that is shown with a 404 error:

<?php
header('Location: https://www.новый-урл.ru".$_SERVER['REQUEST_URI']');
?>

Where is the error in the code?

Answer 1

Lots of quotes?

header('Location: https://www.новый-урл.ru'.$_SERVER['REQUEST_URI']);