Problem Description

Expected: overnode.zulipchat.org

Proposed Solution
If the entered string does:

• match the organization url conditions (Subdomain can only have lowercase letters, numbers, and dashes.)
  • (including) doesn't start with a protocol (https://overnode should still work)
  • (including) doesn't contain any dots, aka any TLDs.

If the URL will be autocompleted, Show that within the text box (with grey text?).

Describe alternatives you've considered
Give the user a first time impression of ERROR?

I might attempt to close this myself within tommorow - 3 months