Service Provider ― DuckDNS (select from the dropdown)
Hostname ― insertanytextwithoutspaces (I normally put in my sub-domain names in one word, for example subdomain1andsubdomain2)
Username/Email ― sub-domain names separated by commas (example subdomain1,subdoamain2)
Password ― token from the DuckDNS site (this is the very long alpha numeric token that DuckDNS provided you when you logged in)
Things to note about the dynamic DNS support:
Your "username" is going to be the name of the record that has been tagged dynamic. ie You marked the A record for dyn.example.com as dynamic. Your username will be "dyn.example.com"
You can tag an A or AAAA record by editing it once you have selected the zone. (check the box).
Once you have "activated" the record to be dynamic, you will need to generate a key (or password if you prefer) for it. (click on the generate icon) to generate the key for the dynamic record.