Ahh, have you gone into the Flamenco folder on the second PC and run the worker?
From what I can tell the system has 2 exe programs, the Manager and the Worker.
Since you installed the software on 1 PC, my guess is that then also started up the Manager and a Worker (I’d half bet if you restarted that PC, nothing would be there, as it doesn’t run at startup/login).
But you’d need to start the Worker on the other PC and do so any time you want to multi-PC render.
Yes, I have but, still nothing, and also, yes, I do have to run the .exe file to start it.
OK, lets try a test, can you access the web UI of the manager from the second PC?
No, I can not.
OK, so it’s a local network issue then. Something is blocking web IP requests, while shared network drives at least work, so some level of network is working.
You should in theory at least be able to ping it, if so it then more likely comes down to maybe port blocking, or as per the FAQ “Most of the time it’s actually Spotify getting in the way, so make sure to close that before you start the Manager.”
Otherwise it could be the modem/router, depending on how your network is setup or your first theory maybe right, and it’s Windows Firewall.
When I say Windows Firewall, that assumes you aren’t running some other security software, like Norton, etc which could be blocking anything or everything on the Manager PC.
YES! 
Ok, got it! It is almost there. Turns out I ended up having Spotify on my second computer without me knowing (I haven’t used that version before) but, now it says unable to connect because it appears it is being blocked by something:
OK, so that’s progress. I take it the web UI now comes up on the second PC.
In theory the worker on the second PC, should be using that same IP address. So if that manager IP is say 192.168.1.1:8080, then the worker on the second PC should be trying to use that same IP.
If not, force close the worker and start it up again with something like: flamenco-worker -manager http://192.168.1.1:8080/
btw, there’s no need to block out local IP number like 192.168.x.x, that’s a local, non-routable IP address space that is used and re-used by millions+ people around the world. It’s not your external IP address as assigned by the ISP.
A little background info: https://en.wikipedia.org/wiki/Private_network
Thanks! Yes, so, I ended up allowing a connection between the Worker to the Manager (by disabling the firewall for those specific apps) but now, when I test render something, it says this:
I also should mention that I did end up making a configuration file for the Worker so it can find the Manager’s IP address (or the Manager in general).
OK, now it seems we are down to Flamenco itself. If you have setup it up as I think you have, using Shared Storage. Then the Blender file needs to be saved in that shared storage location, along with any required textures, etc.
Then on the Manager PC, open the file from that location and use the add-on to send it to the render manager.
Things like Onedrive, etc are not an option.
I tried sending the packed .blend file to the shared folder and sent the job but, I still get the same issue.
From the quickstart guide, I suspect this is the issue:
Create a directory on some storage, like a NAS, and make sure it’s available at the same path on each computer.
In other words, on the Manager PC, you configured the storage at the initial install time to be something like C:\Flamenco, while on the second PC, it’s F:\
That’s not going to work. Every PC needs to point to the exact same storage location in the same way.
Had you used a NAS, then it would have just been the same network map, but since using a PC to both run the Manager and store all the data, you end up with different drive paths.
Basically, on the Manager PC, you need to map F: to the local drive storage and then re-configure the Manager to use the new mapped drive.
So, how do I do that?
In theory you already have the storage shared (to allow the other PC to access it).
So following this procedure: https://answers.microsoft.com/en-us/windows/forum/all/turning-a-folder-into-a-drive-letter/13b42aa7-1ea8-43ba-90f7-751eb10deaa7
You can take that local shared folder and map it to the same drive letter as on the second PC.
On that note, it’s 4am here, so I’m heading to bed.
Then prepare yourself to be amazed. It’ll just work. Just configure Flamenco to use that particular Blender executable (you’ll have to give it the path, of course), and it’ll work just fine.
Really, Blender does not have to be “installed” for Flamenco to run. Flamenco Worker not finding its Manager has nothing to do with Blender itself. At all.
Ahh, OK, good to know.
Then I guess the part from the quickstart list isn’t totally accurate then.
Install Blender on each computer you want to render on. It should be in the same place everywhere.
It’s more a convenience and ease of maintenance thing.
Yup, it took a bit of time but seems we worked out all the networking issues that was preventing that.
Having not actually installed or used it myself yet (only really have one PC so far) I was troubleshooting a little in the dark.
Still, thanks for the software, if/when I need it myself, the new version looks much easier to install and use.
Just wanted to clarify some extra information to what was said by @ArchVisions above that adding a flamenco-worker.yaml file to the local worker install folder (i.e the same directory as flamenco-worker.exe) was the way I avoided any auto-connection issues to the manager.
The contents would be as follows.
manager_url: http://webaddressfromflamencosetup:####/
task_types: [blender, ffmpeg, file-management, misc]
the #### would be the port number (also provided on setup)
This is documented very clearly here too - https://flamenco.blender.org/usage/worker-configuration/
Thanks for everyone who helped. I just want to say the issue is now resolved. To anyone who comes across the issue, make sure you don’t have Spotify on your system as that will block the connection and make sure the path for Blender on the flamenco-manger.yaml is set to the shared storage drive. 
Sure, it’s one of the possible ways of going about things, and the most convenient one. On Windows it associates itself with the .blend file extension, which Flamenco uses to find Blender, so you don’t need to configure any path of the Blender executable if you work that way.
This is a ‘quickstart’, not an ‘in-depth explanation of all the possible things’. It’s accurate, just not exhaustive.
Yup, it took a bit of time but seems we worked out all the networking issues that was preventing that.
Uhu, running a render farm on a network still requires a little bit of networking knowledge.
Thanks for helping out