Currently Knack does not support using any SSL certificate with the Custom Domain feature. This is by now - due to new european legislation and ssl requirements by Crome etc. -a must! Given the many (design) issues, Knacks ‘workaround’ by embedding an app, is not always advisable or workable. Nor does the url structure, see the page tree in the builder, show.
Please provide ssl with custom domain feature, otherwise this valuable feature will become obsolete!