Solved..
I've updated the ownership of below folders and all files under it..
sudo chown -R pi:pi /home/pi
sudo chown -R pi:pi /opt/retropie/configs

it fixed the issue, when IP or any change such as C or H , has been made on netplay setup . it wasn't update the "netplay_ip_address = " in retroarch.cfg accordingly.

thank for helps.

@saccublenda said in Netplay help:

@UberLumby You can follow the instructions here.

Thank you
"Create a symbolic link to the RetroArch core you want to use for netplay in the directory where the core info file was stored, for example
ln -s /opt/retropie/libretrocores/lr-fceumm/fceumm_libretro.so $HOME/.config/retroarch/cores"
This confused me a bit but I think I understand this creates a link to the existing .So I was copying and pasting them into the retroarch cores folder last night lol ops...

Check your port forwarding settings on your router. You maybe able to restrict the port forward to specific external IP address(es) or MAC address(es). If so you can whitelist your friends IP/Mac address.

@Kaydron said in Issues with NetPlay: Client cannot connect when going through RetroPie:

I found this post that has very similar symptoms https://github.com/RetroPie/RetroPie-Setup/issues/3161.

If you're encountering the same problem as the the one described in the issue, then there's no solutio yet, just the workaround posted in the same issue. The only method that seems to work is to directly connect by specifying the hostname.

@BGallagherLA wondering if that is just an automatic thing with NetPlay and is just a computer player or something rather than someone actually joining? I just don't understand how someone can randomly join a game when you need the proper external IP to be able to access the game, and the exact same rom set, emulator and RetroPie version in order for it to work

Instructions were added to liberatro document site:
https://docs.libretro.com/guides/netplay-multiple-controllers/

@saccublenda Brilliant, thank you. My friend has been having 'port mapping failed' issues (as well as the 'failed to initilise Netplay' one which seems to be what this thread is trying to address) so will try with the relay I think. This is all very new to me - tried hosting earlier to see what happened (with relay on) and it told me I had connected to Nick!! No idea what I'm doing really 🤣

@mitu Thank you. That's all I needed to know.

@Daistaar said in Netplay questions: Can two Pi's connect directly via LAN?:

Would this allow, say full screen multi-player Mario Kart for each monitor? Would they still just see everything split?

That would require heavy hacking on the game roms themselves, while RetroArch's Netplay just uses the unmodified roms and spans the players' monitor & controller cables through the network, figuratively speaking.

@Efriim said in Error when starting netplay host:

@saccublenda
Perhaps there is the same setting somewhere within retroarch.

Indeed there is. Under Settings -> User -> Username (it sets the "netplay_nickname" in
retroarch.cfg). With this matching the hostname I can start the netplay host from retroarch menu.

It is a peculiar thing, I remember it working without configuration, I had a hostname so I don't really understand it.

Same here. I used to have a netplay nickname different from the hostname, and it didn't matter. Weird.

@mitu said in Can't seem to get Netplay to work:

@mikespie Please add more info about your system - https://retropie.org.uk/forum/topic/3/read-this-first.

The core means which emulator are you using for the running the game. You need to use the exact version of it and also the exact ROM on both systems. Since you're running a Megadrive rom, the core should be either lr-picodrive (I think this is the default) or lr-genesis-plus-gx (see the Megadrive docs).

Thank you for your response, sorry for not providing all info. Just from your post I was able to figure it out and have Netplay working / connecting now! However, it seems as though the controllers do not work in a lot of the games while on Netplay. I have tried using different emulators to no avail. An example is Street Fighter II for Genesis, Player 1 controller works fine, but player 2 controller doesn't work at all. Tried a keyboard as well, both which work fine not in Netplay.

My system is a CanaKit - https://amzn.to/2Taj5jf
PI 3 B+ w/ 2.5A power supply
RetroPie V 4.4.4 (skyscraper-pr6-v3)
Built from premade SD image on RetroPie website
I have a USB keyboard, mouse and controller hooked up to it
Controller is working great outside of Netplay, it's an "EasySMX 2.4G Wireless Controller" and also a Geeekpi SNES USB controller
Emulator is lr-genesis-plus-gx

Thanks again!

shot out of left field here, but did you ever end up figuring this out? same issue and the web is completely barren of references to the issue apart from yours lol

@madmodder123 Cheers. Have you used Netplay outside of a LAN type situation? I've heard it's optimized for LAN use and doesn't work well over the interwebs.

@revlied

Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first

Along with the information requested there, what part of the Netplay documentation seems outdated?