How to stop connection rejection

[minitech]

I get an error saying that the connection was rejected by the target machine here, suggesting that my firewall is working well

How do I make sure that the connection is accepted? It's a chat program (obviously) so I'm going to need to do the same thing on users' computers when it is installed. How do I make this in such a way that the connection will be accepted but leaving security uncomprimised?

Imports System.Net.Sockets
Public Class QuickChat
    'Dim invited As List(Of String) = New List(Of String) 'ip addresses
    Dim ip(3) As Byte
    Dim conn As NetworkStream
    'Dim s As Socket
    Dim tcpclient As TcpClient
    'Dim tcplistener As TcpListener
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Set up form
        Dim si As Size = Screen.GetWorkingArea(New Point(1, 1)).Size
        Me.MaximumSize = New Size(si.Width \ 3, si.Height)
        Me.Width = Me.MaximumSize.Width
        'Retrieve chat IP.
        Dim ipre As New System.Text.RegularExpressions.Regex("^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$")
        Dim cip As String = InputBox("Please enter the IP address of the person that you would like to send to.", "Enter IP Address", "0.0.0.0")
        If Not ipre.IsMatch(cip) Then
            Me.Close()
            Exit Sub
        End If
        Dim ipbs() As String = cip.Split(".")
        ip(0) = CByte(ipbs(0))
        ip(1) = CByte(ipbs(1))
        ip(2) = CByte(ipbs(2))
        ip(3) = CByte(ipbs(3))
        'Set up send/recieve
        tcpclient = New TcpClient()
        tcpclient.Connect(New Net.IPAddress(ip), 120)
        conn = tcpclient.GetStream()
        Me.tmrCheckForMessage.Start()
    End Sub
 
    Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click
        SendMsg(Me.txtNewMessage.Text)
    End Sub
    Private Sub SendMsg(ByVal msg As String)
        Dim c As Char
        For Each c In msg
            conn.WriteByte(AscW(c))
        Next
        conn.WriteByte(0)
    End Sub
    Private Function GetMsgIfAny() As String
        Dim b As Byte = conn.ReadByte()
        Dim str As String = ""
        While b > 0
            str &= ChrW(b)
            b = conn.ReadByte()
        End While
        Return str
    End Function
 
    Private Sub tmrCheckForMessage_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tmrCheckForMessage.Tick
        Dim s As String = GetMsgIfAny()
        If s = "" Then Exit Sub
        Me.txtChatLog.Text &= String.Format("{0}{1}{0}{0}", ControlChars.CrLf, s)
    End Sub
End Class