Thank you for supplying the information you have. There is probably additional detail available for the error you received. Can you post the full response, if there’s more.
edit: I looked at the Icewarp logs and I found the error:
ACME Exception: Error requesting challenges 403 urn:acme:error:unauthorized Error creating new authz :: Validations for new domains are disabled in the VI API
Your ACME client is outdated. You need an ACMEv2 client. There are a number of choices, including by own (Open ACME), though it is currently being updated.