Each aircraft receives its own radar transponder code, which the pilot enters in the cockpit. To do this in a coordinated way, a web application was created that allocates codes using the same algorithms as in reality.
Scumari Technologies has made an online application that assigns radar transponder codes to aircraft located in the Slovenian airspace. It uses the codes that are assigned in reality. The link leads you to a web site with a built-in application. Keep the site open while you are online. It is required to use it. You need to log in with your IVAO ID.