I teach an "Intro to Web Development" course and routinely have my students submit the URL where they have uploaded files for an assignment (using the "Submission Type -> Website URL" option). Often, my students submit invalid URLs which Canvas nonetheless accepts, creating complications because the assignment deadline has passed and students have lost time they needed to correct their inability to upload files. There are other situations in which this same issue will be problematic.
I will attach a screenshot with an example of what I frequently see, involving a URL obviously located on someone's computer vs. the internet. With or without an http: (or https: or ftp:) prefix, basic error trapping for this FI request can be easily accomplished by just assuring that a valid domain name is involved.