The error shown when you try to add a link that is longer than 1000 characters to a custom section in the sidebar is difficult to read because it’s larger than the modal.
Example link:
/new-topic?&title=Lorem%20ipsum%20dolor%20sit%20amet&body=Lorem%20ipsum%20dolor%20sit%20amet%2C%20consetetur%20sadipscing%20elitr%2C%20sed%20diam%20nonumy%20eirmod%20tempor%20invidunt%20ut%20labore%20et%20dolore%20magna%20aliquyam%20erat%2C%20sed%20diam%20voluptua.%20At%20vero%20eos%20et%20accusam%20et%20justo%20duo%20dolores%20et%20ea%20rebum.%20Stet%20clita%20kasd%20gubergren%2C%20no%20sea%20takimata%20sanctus%20est%20Lorem%20ipsum%20dolor%20sit%20amet.%20Lorem%20ipsum%20dolor%20sit%20amet%2C%20consetetur%20sadipscing%20elitr%2C%20sed%20diam%20nonumy%20eirmod%20tempor%20invidunt%20ut%20labore%20et%20dolore%20magna%20aliquyam%20erat%2C%20sed%20diam%20voluptua.%20At%20vero%20eos%20et%20accusam%20et%20justo%20duo%20dolores%20et%20ea%20rebum.%20Stet%20clita%20kasd%20gubergren%2C%20no%20sea%20takimata%20sanctus%20est%20Lorem%20ipsum%20dolor%20sit%20amet.%20sadipscing%20elitr%2C%20sed%20diam%20nonumy%20eirmod%20tempor%20invidunt%20ut%20labore%20et%20dolore%20magna%20aliquyam%20erat%2C%20sed%20diam%20voluptua.%20At%20vero%20eos%20et%20accusam%20et%20justo%20duo%20dolores%20et%20ea%20rebum.%20Stet%20clita%20kasd%20gubergren%2C%20no%20sea%20takimata%20sanctus%20est%20Lorem%20ipsum%20dolor%20sit%20amet.