Next step, as this might be a DuckDNS ‘handshake and IP verification’ issue.
Here are my settings … it is sufficient to just enter ‘nouser’ as a Username, as DuckDNS just uses the Domain and their Token as a Password to validate. Ensure you are using the Token that appears on your DuckDNS web login page and not your regular Google password.
More importantly, try http://checkip.dyndns.com as the URL to detect … see if this makes a difference
Be aware that sometimes there can be a small delay for the DDNS to update, so wait a little before checking.