That dongle is used to protect RAPT against illegal use and as anti-piracy measures. This is a standard practice in this area. The dongle also protects the sales by turning pirates into customers. Of course, the dongle might be bypassed, but that's not the point.
You will need to contact the developers as they and ask how to use the program without the dongle, I mean to buy it digitally and use a serial number or alternative to register it.
General Email: firstname.lastname@example.org
Sales Email: email@example.com
Support Email: firstname.lastname@example.org