remote access not working

Hi Guys, racking my brain trying to get plex to work remotely with no luck. I,m using a qnap 231+ nas to run the plex server.
I am using a Pakedge RK-1 High end router which is DMZ thru a Bell Modem, I’ve opened port 32400 and i,ve confirmed vie “port checker” that its open. I have enabled “:remote access”. But fails the connection.
It works perfectly on the local LAN.
All the qnap apps i have for remote access work perfectly, seeing the files via qfile etc so I know its related to plex somehow.
Any thoughts, greatly appreciate the help.
glenn