Please make sure to append the query parameter with a '?' question mark to the URL if there are no other query parameters present and with a '&' if the URL already has query parameters.
Your Url should look something like this:
https://www.example.com/space/page-123.html?X-Scroll-Viewport-Enable-Performance-Statistics=true
https://www.example.com/space/page-123.html?parameter=true&X-Scroll-Viewport-Enable-Performance-Statistics=true