~~Jumping into this as having the same issue.
'Dedicated' server. AKA, 3rd PC that isn't trying to play Tarkov at the same time.
Server and one of the clients are on the same LAN, 2nd client is on a different network.
If a single player tries to start a raid, it works fine.
If a player tries to host a multi-person raid, it just gets stuck on "Waiting for 'X' Players.
I've turned off the Windows firewall on both clients.
And turned off the Windows firewall on the Server.
I've port forwarded both 6969 TCP and 25565 UDP to my server IP.
One thing I have noticed, is the below from the output on the server console when a multi-person raid is hosted. Though, unsure if this is related.
TypeError: Cannot read properties of undefined (reading 'players')
at MPTMatchService.removePlayerFromMatch (S:\Tarkov-SP\user\mods\mpt-server\src\services\MPTMatchService.ts:323:34)
at MPTRaidController.handleRaidLeave (S:\Tarkov-SP\user\mods\mpt-server\src\controllers\MPTRaidController.ts:60:30)
at MPTRaidCallbacks.handleRaidLeave (S:\Tarkov-SP\user\mods\mpt-server\src\callbacks\MPTRaidCallbacks.ts:33:32)
at RouteAction.action (S:\Tarkov-SP\user\mods\mpt-server\src\routers\static\MPTRaidStaticRouter.ts:33:50)
at MPTRaidStaticRouter.handleStatic (C:\snapshot\src\di\Router.ts:47:63)
at HttpRouter.handleRoute (C:\snapshot\src\routers\HttpRouter.ts:79:62)
at HttpRouter.getResponse (C:\snapshot\src\routers\HttpRouter.ts:44:30)
at HttpRouter.getResponse (S:\Tarkov-SP\user\mods\mpt-server\src\overrides\routers\HttpRouter.ts:25:52)
at AkiHttpListener.getResponse (C:\snapshot\src\servers\http\AkiHttpListener.ts:150:38)
at IncomingMessage.<anonymous> (C:\snapshot\src\servers\http\AkiHttpListener.ts:75:43)
TypeError: Cannot read properties of undefined (reading 'players')
TypeError: Cannot read properties of undefined (reading 'players')
at MPTMatchService.removePlayerFromMatch (S:\Tarkov-SP\user\mods\mpt-server\src\services\MPTMatchService.ts:323:34)
at MPTRaidController.handleRaidLeave (S:\Tarkov-SP\user\mods\mpt-server\src\controllers\MPTRaidController.ts:60:30)
at MPTRaidCallbacks.handleRaidLeave (S:\Tarkov-SP\user\mods\mpt-server\src\callbacks\MPTRaidCallbacks.ts:33:32)
at RouteAction.action (S:\Tarkov-SP\user\mods\mpt-server\src\routers\static\MPTRaidStaticRouter.ts:33:50)
at MPTRaidStaticRouter.handleStatic (C:\snapshot\src\di\Router.ts:47:63)
at HttpRouter.handleRoute (C:\snapshot\src\routers\HttpRouter.ts:79:62)
at HttpRouter.getResponse (C:\snapshot\src\routers\HttpRouter.ts:44:30)
at HttpRouter.getResponse (S:\Tarkov-SP\user\mods\mpt-server\src\overrides\routers\HttpRouter.ts:25:52)
at AkiHttpListener.getResponse (C:\snapshot\src\servers\http\AkiHttpListener.ts:150:38)
at IncomingMessage.<anonymous> (C:\snapshot\src\servers\http\AkiHttpListener.ts:75:43)```
UPnP shouldnt be required due to the port forwarding. UPnP is basically a (less reliable) automatic port forwarding. If you've done it manually, it's not needed.~~
Port forwarded 25566 and in F12 set port to 25566, all good now.