I am trying to add a Page Rule to redirect a URL to a shared Google Sheet. I was getting an error message saying the sheet I am linking to is no longer available. I realize when I click Save and Deploy in the Page Rule box it drops the case of the redirect URL thus breaking the link as Google differentiates between capital and lower case letters. Is there anyway to preserve the copied URL and make it case sensitive?
I can reproduce this, a page rule with a forwarding URL lowercases the forwarded URL. I guess this is a bug and there might not be much you can do at this point (until it is fixed).
Until then, move the forward from Cloudflare to your webserver (htaccess if you are using Apache).