IPN stands for Instant Payment Notification.
You can connect autoresponder, membership sites and other systems to DigiStore24 with it.
For all other systems DigiStore24 provides a generic connection. With it you can connect your system via an easy usable HTTP interface.
In DigiStore24 you set your connection via Settings > IPN.
Experienced software developer embed their own system within a short time.
More information about it here: