You might try updating to Certbot 2.3. There was a bug fix in 2.3 for this error but I can't know for sure if this fixes your situation. See the link below for details
Or, as rg305 suggested, just do a manual request if this is just a one-time cert. The manual-auth-hook with acme-dns is for automating cert renewals when your domain name service does not provide an API to do so (or, you just prefer to do it this way).