Port forwarding issue on NightHawk AX3000 RAX36S

I just purchased NightHawk AX3000 and trying set it up and ran into issue.

It is not letting me forward 2 external ports (443 & 8123) to one internal port of 8123 of an internal ip address 192.168.1.x. I need this for home assistant. All the routers that I have used(TP-LINK, ASUS), lets me do that but Nighthawk is saying Conflict in rule.

It lets me set one forwarding like this..

Now if I try adding external port 8123 to 8123 on same IP address as another rule, it throws error.

I tried disabling UPnP but has not helped. Any idea why? or is it just the limitation of the router? Error message