You can’t attach from a URL. So https://ucarecdn.com/8aa17c61-bd55-4311-8b45-7d9a2efde6c5/ won’t work.
You need an absolute path to the file, such as /path/to/my/file.ext.
But there are some other problems with your code snippet as well. You use $email_attachement (with a ..chement…) in one place, but then $email_attachment in your wp_mail() call. Also, your “attachment” isn’t a file. While that may resolve as a URL, that would involve a URL rewrite which isn’t going to work for accessing a file to attach.