@Mikey_H 

I have the latest firmware, but it worked before as well. 

I have set my username and password in the app. I am using for example an app called Onvier on my android box and I we have it turned on on our tv.

For my ip, I have ip:2020 port. I think the port is default and I have used my router to set a fixed local ip.

So, example would be 10.10.10.20:2020. Username and password as setup in the app.

I have used IP Cam Viewer Full on my fire tv and it was the same.

The only thing is RTSP URI: rtsp://ip:554/stream1

I hope it works out in the end for you.

  @Solla-topee 

Hi and thanks for your reply.

I noted in a thread on https://linustechtips.com/topic/1499641-cant-access-rtsp-streams-from-outside-network/:

"Actually it wasnt the cameras, it was the router it seems. For anyone reading this and having the same issue: turns out my router (TP-Link Archer C80) was messing with the RTSP traffic or at least that is what it seems. Went to the web gui -> Security -> ALG and turned off RTSP ALG. Problem solved. Thanks for your suggestion tho, doing a Wireguard tunnel is not a bad idea for privacy concerns. In my case its just a RTSP Stream aiming at the traffic light near my house so Im not that concerned about someone taking a look into it "

I noticed the Deco app does have SIP ALG - can we add other common Application Level Gateways - IPSec, RTSP, PPTP as well as SIP as available in other routers?