DMZ Question

I am trying to enable DMZ on my Cox router. No matter what I do, whenever I click edit, then enable DMZ, under the advanced setting, the Cox WiFi app gives the following error “We Encountered an Issue. if the problem persists, check back later.Try Again.” I have then have to close the app and start over.  I also tried changing the setting in the router web portal, but the setting for DMZ says to use the Cox WiFi App. I have reinstalled the Cox WiFi app on two different mobile devices to make sure it was not a corrupted app  
I have swapped 3 panoramic modems in week, now I am using the latest Cox XB8.  I was recommended by tier 1 help desk to purchase the Cox Complete Care to assist me. Compete Care suggest I swap out to the newest XB8 as DMZ had been deprecated in the older Cox WiFi router. 
Sadly, I am getting the same error as before.  I am at a loss. Does anyone have any suggestions? I need DMZ and not port forwarding.  I have included 2 links below on imgbb for the screenshots of the Cox WiFi app error. Just enter the imgbb url and then add a forward-slash and the image name below. Thank you in advance. 

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