iPhone doesn't connect to the web socket but the simulator does - swift

Question

Physical devices cannot connect to my web socket. I tried it with 3 different phone and with different networks. It works fine with my simulators though. I am not getting an error message apart from the standard "Cannot connect to the server" from socket.io on the client.
I don't know if this is a valid indicator but I also tried using https://www.websocket.org/ with the following parameter:
wss://converzone.htl-perg.ac.at:5134
I am getting a "ERROR: undefined DISCONNECTED" there.
I am using an ubuntu server which runs Ubuntu 16.04. The web socket is from socket.io and I am coding with Swift on the client and with Node.js on the server. This whole thing is running on my school's server.
// Here is an array of all connections to the server
var connections = {};
io.sockets.on('connection', newConnection);
function newConnection(socket) {
console.log(socket.id + " connected.");
socket.on('add-user', function(user) {
connections[user.id] = {
"socket": socket.id
};
});
socket.on('chat-message', function(message) {
console.log(message);
if (connections[message.receiver]) {
console.log("Send to: " + connections[message.receiver].socket);
//io.sockets.connected[connections[message.receiver].socket].emit("chat-message", message);
io.to(connections[message.receiver].socket).emit('chat-message', message);
} else {
console.log("Send push notification")
sendPushNotificationToIOS(message.senderName, message, message.deviceToken, message.sound)
}
});
//Removing the socket on disconnect
socket.on('disconnect', function() {
console.log("The client disconnected");
console.log("The new list of clients is: " + connections)
for (var id in connections) {
if (connections[id].socket === socket.id) {
delete connections[id];
break;
}
}
})
}
Please understand that this problem seems very weird to me. I have changed the AppTransferProtocol in my plist and changed the port from 3000 to 5134. Nothing changed. Tell me what code would seem relevant apart from the (minimal) server code.