TCP/IP Indy Chat Delphi 10.3.3 FMX (using internet, not only LAN)

  

I tried making a simple chat system in Delphi 10.3.3 Community Edition using FireMonkey and the Indy components TIdTCPClient and TIdTCPServer.
It works fine if the Client and Server are located in the same WiFi network (Server = Windows 10 and Client = Android 10). I used the computer’s IPv4 address shown in ipconfig to get the computer’s IP, and my mobile phone successfully connects.
But, if I use the internet IP (got it from https://www.whatismyip.com/de/), the client shows the german equivalent to "socket error # 111 connection refused", so what am I missing? I entered the IP in the edit box to connect to – so if the local IP works, why doesn’t any other IP work as well?
Here is the code I used:
unit Unit1;

interface

uses
System.SysUtils, System.Types, System.UITypes, System.Classes,
System.Variants,
FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs, FMX.StdCtrls,
FMX.Controls.Presentation, IdCustomTCPServer, IdTCPServer, IdBaseComponent,
IdComponent, IdTCPConnection, IdTCPClient, IdContext, FMX.ScrollBox, FMX.Memo,
FMX.Edit;

type

TForm1 = class(TForm)
GroupBox1: TGroupBox;
GroupBox2: TGroupBox;
Button1: TButton;
IdTCPClient1: TIdTCPClient;
IdTCPServer1: TIdTCPServer;
Edit1: TEdit;
Edit2: TEdit;
Memo1: TMemo;
Edit3: TEdit;
procedure Button1Click(Sender: TObject);
procedure IdTCPServer1Connect(AContext: TIdContext);
procedure IdTCPServer1Disconnect(AContext: TIdContext);
procedure IdTCPServer1Execute(AContext: TIdContext);
private
{ Private-Deklarationen }
public
{ Public-Deklarationen }
end;

var
Form1: TForm1;

implementation

{$R *.fmx}

procedure TForm1.Button1Click(Sender: TObject);
begin
IdTCPClient1.Host := Edit1.Text;
IdTCPClient1.Port := StrToInt(Edit2.Text);
IdTCPClient1.Connect;
if IdTCPClient1.Connected then
begin
IdTCPClient1.IOHandler.WriteLn(Edit3.Text);
IdTCPClient1.Disconnect;
end;
end;

procedure TForm1.IdTCPServer1Connect(AContext: TIdContext);
var
ip:String;
begin
ip:=AContext.Binding.PeerIP;
TThread.Synchronize(nil,
procedure
begin
Memo1.Lines.Add(‘connect: ‘ + ip)
end);
end;

procedure TForm1.IdTCPServer1Disconnect(AContext: TIdContext);
var
ip:String;
begin
ip:=AContext.Binding.PeerIP;
TThread.Synchronize(nil,
procedure
begin
Memo1.Lines.Add(‘disconnect: ‘ + ip)
end);
end;

procedure TForm1.IdTCPServer1Execute(AContext: TIdContext);
var
msg:String;
begin
msg:=AContext.Connection.IOHandler.ReadLn;
TThread.Synchronize(nil,
procedure
begin
Memo1.Lines.Add(‘message: ‘ + msg)
end);
end;

end.

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