Not sure if anyone is too familiar with PlayIt but I asked around in their discord too and couldn't get a solid answer. The dedicated server is running on another PC of mine and can be joined with its local IP so it should be working... PlayIt seems to get the join attempt as it lists an inbound connection when attempting but it seems it can't forward it to Zomboid as the server isn't detectable when trying to join via PlayIt IP/port.
Sometimes it'll seem to forward the connection to Zomboid (it'll show attempting steam connection and authorizing with steam...) but then throw up the "Connection Failed" message anyways. I have no clue how to recreate this as it seems random but when it does happen, the server CMD says that a player, "ID=null, password=null" has attempted to join but then got timed out as it "couldn't be found." Now the server CMD doesn't show any messages when trying to join, as if nothing is even happening.
I've allowed the ports through the windows firewall and the last thing I can think of (but trying to avoid) is to port forward the ports on my router and just skip PlayIt altogether. Only reason I haven't done this is for network security reasons. Any insight would be greatly appreciated! I've been at this for days...