Services->Dynamic DNS->Dynamic DNS Clients-> Cached IP is N/A with Dynamic DNS and No-IP(free)

[axiomcs]

After resetting the Netgate SG3100 box to its factory defaults, I went thru the startup config and left all fields to their defaults. I then added a No-IP hostname and username and password and I changed the Service Type to No-IP(free).
After saving it, the Cached IP shows N/A. If I go to Interfaces->WAN and enter my public IP directly along with IPv4 config type as Static, and then go back to the Dynamic DNS->Dynamic DNS Clients, the Cached IP shows the correct public IP in green.

After entering Service Type and Hostname and Username and Password in the Services/Dynamic DNS/Clients page and saving, should the Cached IP contain the correct public IP in green with the IPv4 Address field being empty for the wan interface?

Any suggestions? Am I missing a setting(s)?

Is Dynamic DNS meant to be setup after the Interface WAN has been setup? Or can Dynamic DNS be setup without setting up the WAN interface?

Update:
It turns that I was trying to setup a Netgate firewall for a location that uses a dynamic public ip from my location which has a static ip.
If I am at a location that uses a dynamic public ip, do I set the WAN interface for a dhcp IPv4 Config Type? Then fill out the Service/Dynamic DNS page? And the Cached IP will contain a green ip after saving the dynamic dns info?