I need to assign public access to my "Chat Server"

Jeff_ATS

I have setup Services, a Service_Group and an Object as follows:

I want to setup pulic access from my WAN port to the Chat_Server

I setup NAT as I think understand it:

mMontana

AFAIK is almost correct. Neverthless, I'd use some different parameters.

Considering how did you grouped services, Virtual Server is close to correct to me.
Also, if your WAN interface is configured with the "User-defined External IP" I'd choose in "external IP" (instead of "User Defined" ) "WAN1_Interface_Host" or… the actual interface that connect to internet and which should be the path to access to your Chat Server.