Hey there!
I don't get it, for real.
It might be 4(!!) weeks by now and in between I figured out many mistakes made by myself coz of just "I don't know how to...".
Also I didn't know: Just "work only" in the batch file, not in the server.cfg alone. *lol*

Running my home Windows 11pro PC as a Rust Dedicated Server and I play on it, too.
So, same machine for DS and playing. Everything's in the Batch file - server.cfg is empty!

My Rust Dedicated Server works, Remote Console (Rcon), also, and I can access it with the tool "RustAdmin".
Great!
I also can see my own DS in favorites in the Steam server list and also ingame favorites and I can clearly see my server.
Awesome!
Also everything works in server header-image and server-information w/o glitches or missing chars or what not.
Super Awesome! Really great!

I also set my Firewall and my ports in my router hopefully correctly ...it seems... (coz I can start in steam/server/favorites/my server to go in my game or via favorites in the already started game)...

...but it seems there's a hook which I cannot figure out what it is.

When I start my DS I can read this in the console and also in my logfile:
Could not establish a TCP connection to 95.x.x.x:28083 0b/s in, 0b/s out

The 95.x.x.x seems my IPS ip and not my home IP which is starting with 192.xxx
(The x's stands for further ip numbers which of course I won't like to show up here)

But a bit before that line above:
"IP address from external API: *.*.*.*
The server is currently listed under Community"
So? So, it seems IP is working, but not the port forwarding? Goooosh, I don't get it! :.-(

That's one problem!

The second problem is when I'm in game.
Ingame I hit ESC, going to "RUST+", click it and....
"this server has disabled the companion app feature"
Gosh! I'm getting more and more desperate!

It's really not about I need the feature, It's about I want to learn how it works and why it does not work and...just why!

I watched so many videos, so many tutorials I've had read and so on and so on, but nothing helps and I stuck, so I hope anyone can help me out of my misery. *sigh*

I read about "you need to activate the app" but I couldn't figure out how.
See here: https://wiki.facepunch.com/rust/rust-companion-server
I my case port 28083 is needed which I've opened in my router (modem is router; aio device).
But it doesn't works.
Logically also the command app.info (via F1 console) isn't working, too. It does literally nothing.
"companion.id" in my Rust folder is there.

"+app.port 1" is active in my BAT but it doens't matter if the line is there or not. It has no effect.

And so far I know I don't need that anymore? (idk)

In the article above there's a line: "Automatic connectivity testing"
So, in my server log file I got this message:
"Rust+ companion server connectivity test failed! Disabling Rust+ features."

Well, I read more in the article:
"To fix this error message you will either need to configure your server so that the test passes or..."
I won't "or", I want the solution. *laugh*

Maybe anyone can help me out? Has an idea? A solution?
Maybe I miss something in my Bat or router or firewall or or or....idk

Sincerely, Tinkerbell

A long-winded question, but to get your Rust+ working you need to set up your port forwarding properly for port 28083 and also make sure your firewall isn't blocking it.

The Rust+ port is the only one that is "checked" during server startup (from outside your network). If the port doesn't respond during startup then Rust+ is automatically disabled.

Hey JimDeadlock!

Thank you for your kind reply. Yes it is really hard to get through it and I must admit I don't get it. I guess I have to live with that.
So, yes I gave up on that. 
But maybe in a few months or years someone has a solution or I find a way, so the thread could stay open.

Sincerely, Tinkerbell 

Merged post

Soooo, I got it! Problem is solved, although not solved. 🧐

It just does not work, because:

I have DS-Lite Tunnel only in my Router.

For using port forwarding I need at least Dual Stack, so I can use iPv6 AND iPv4 which means in conclusion:
"Services" like Rust+ needs the iPv4 protocol and it can't handle ipV6 protocols. (as far I know in July 2024)

In other words:
My ISP handles v4 ip's like forwarding to v6 with Dual Stack Lite Tunnel (DS Lite).
But, as mentioned, I need a clearly to see iPv4 adress which I can't because my ISP just isn't providing it.

To everyone else:
If your port forwarding is not working (you can test it like I did: https://www.yougetsignal.com/tools/open-port ), you will need to call your ISP to enable Dual Stack. (so that you not only get an clearly to see iPv4 IP but can also use iPv6 at the same time.)

In short, regarding Rust and Rust+ (and obviously also some other software/games, too):
DS means you can access your computer via the Internet.
DS Lite (Tunnel) means you can NOT access your computer via the Internet.

In my personal case it is just not possible. 😢

I'm using FRITZ!Box 6591 Cable.

But YES, there COULD be a simple solution. Read the following bold paragraph!
It is mentioned here: https://avm.de/service/wissensdatenbank/dok/FRITZ-Box-6591-Cable/1611_Was-ist-DS-Lite-und-wie-funktioniert-es
Translated with google to english:

Dual-Stack Lite (DS-Lite) is a method that allows applications that use the Internet Protocol v4 (IPv4) to be used on Internet connections via the Internet Protocol v6 (IPv6). DS-Lite is used by Internet providers who do not have enough public IPv4 addresses for their customers and therefore set up IPv6 Internet connections for them using DS-Lite.
On a DS-Lite Internet connection, the FRITZ!Box packs all data from IPv4 applications into IPv6 packets and sends them to the Internet provider via the IPv6 connection (IPv4-in-IPv6 tunnel). There, a special server unpacks the IPv6 packets and forwards the IPv4 data they contain to the actual destination on the Internet.
With DS-Lite, almost all IPv4 applications can be used without restrictions.

Only access to the FRITZ!Box or devices in the home network via the Internet is not possible via IPv4, as the FRITZ!Box does not receive a public IPv4 address from the Internet provider. Servers operated in the home network cannot therefore be reached from the Internet via IPv4.

Such connection problems can be solved with the Port Control Protocol (PCP). With PCP, the FRITZ!Box can set up port forwarding for itself with the Internet provider and thus bypass the missing public IPv4 address. The FRITZ!Box already supports PCP and the first providers of DS-Lite Internet access could support PCP over the course of the year.

Note: Internet access to the FRITZ!Box and home network is also possible via IPv6 on the DS-Lite Internet connection. However, such IPv6 connections can only be established if both participants have an IPv6 Internet connection, which is not the case in all mobile networks and WLAN hotspots, for example.