I've seen a few other folks report the same issue when setting up their landing page, and I believe in all cases this was something that the ConvertKit support folks needed to resolve. I'd suggest you reach out to ConvertKit's support team at help@convertkit.com37 (or with the message bubble in the lower right corner) and they should be able to get this handled.

Aaron HockleyCommunity Guru
Photographer, Writer, Consultant