Starting ProFTPD...
 Checking syntax of configuration file
 /Applications/XAMPP/xamppfiles/proftpd/scripts/ctl.sh : proftpd started

1. Open the file /Applications/XAMPP/etc/proftpd.conf

2. Search for the port "21" and change it to some other port (e.g 28).

3. Open the file /Applications/XAMPP/xamppfiles/xampp

4. Search for the port "testport 21" and replace it to "testport 28".

5. Now go and run "sudo /Applications/XAMPP/xamppfiles/xampp start". (It should work now).