I don't believe there is any validation on the URL. I don't see the error you are receiving in your post, but I suspect the failure is unrelated to the URL. Edit after screenshots:
The SCIM client is making a GET call querying if a specific user exists. That user is not expected to exist, as this is just a functional test of the server during credential validation. Any query on /Users that is syntactically correct and isn't using non-existent parameters or attribute names should return a 200/OK, not a 404.
Your server is returning a 404 which is the issue.