Step number one, install SRT package for the Nimble streamer. Log into the server SSH and run (if using Ubuntu):
sudo apt-get update; sudo apt-get install nimble-srt; sudo service nimble restart;
Other distros have tutorials here: https://wmspanel.com/nimble/srt_install

Select the port you want to use for SRT, lets say 2222.
Open port 2222 on the firewall for the server.

I'm also using WMSPanel in addition to the Nimble Streamer to have a nice GUI for it. But it can be done on the server side as well.

Add MPEGTS SRT stream:

• Receive mode: Listen
  
• Local IP: 0.0.0.0
  
• Local port: 2222
  
• Alias: SRT stream for port 2222 - you can select your own
  
• Latency: 400 - good to setup something here, if you want to force as low vMix can go with the latency. Lets say you set it to 1000 and someone wants to send stream with latency 125ms, then 1000ms will be used. But if someone setups vMix to send 2500ms latency, 2500ms latency will be used. Bigger wins.
  
• maxbw - you should setup it when sending SRT stream between Nimble instances to keep Nimble from using too much bandwidth. For vMix it does not matter since vMix does it on its end.
  
• Add outgoing stream checked, insert your application name and stream name where you want your RTMP stream to sent on the Nimble
  

You're done. You probably messed up the Local IP setting. 0.0.0.0 listens on all the network interfaces server has, if you use your local IP or 127.0.0.1 then you can send SRT to it only from the server itself. Nimble does not support Stream ID at the moment, so you will need to create multiple "ports" for multiple SRT inputs if you need that. You can also send me a PM regarding your contact info, I can help you setup it if you are not using WMSPanel.

I will take a moment at one point to write in depth guide for it as well in the forum.

A guide for that would be awesome. ;) I don't get it running, with or without 0.0.0.0 ...
I'm using WMSPanel with Nimble and my server is a Google Cloud machine. Can you show screenshots of your settings in VMix and WMSPanel? :)

Thanks and regards
Seb

EDIT: It was just the firewall on the target machine. Now it works... :)