I did set up a reservation but the Ubiquiti cloud gateway Ultra that I'm using is a little convoluted in setting that up and initially it seemed like it wasn't possible. After doing a bit of research and reading I was able to figure it out. Normally I would just go into the DHCP server and set up the address reservation in advance so I can create the necessary port forwarding. With the Ubiquiti cloud gateway you need to connect the device, then once it has an address go into another screen to set the IP address to "fixed" which creates the reservation. Then I was able to create the port forwarding rules.
I just like to have things with special routing and port forwarding to have fixed IPs...it's an old habit.
I understand the hazards of fixed IP's so I get why it's greyed out. A tool tip that pops up when yo try to unblock it with a message would be helpful. May be in a future version.
Thanks for your quick response.