Improve error message for bad URL or form/link state

[lognaturel]

This is currently entirely handled by the host application and likely will continue to be.

Proposal: replace all the error states below with a single full-page message (see current styling for #813, note there is no close action):

Unable to open form

Please check that the link is correct. The form may no longer be available, or your access may have expired. If the problem continues, contact the person who sent you the form link.

Invalid enketoid

Current behavior: snackbar at bottom of blank page says "No Form found with this URL, please double check."

Invalid st query parameter

The st query parameter uniquely identifies a Public Access Link. Under the hood it is an auth token.

Current behavior: snackbar at bottom of blank page says "Could not authenticate with the provided credentials."

Loading closed form or revoked Public Access Link

Current behavior: snackbar at bottom of blank page says "The authentication you provided does not have rights to perform that action."

Context: submitting to closed form

For reference, here is the message shown when attempting to submit to a closed form:

This seems ok to me. I would change "the person who asked you to fill this Form" to "the person who sent you the form link."

Design

Edit 2nd June 2026: Design ideas in Figma