(See FAQ Registration Code)
The registration token can be used to create a registration code for a user. This registration code can be sent via postal mail to the user, so that the user can use this registration code as a second factor to login to a portal.
After a one single use, the registration code is deleted and can not be used a second time.
The length and the contents of the registration code can be configured using the Enrollment policies registrationcode_length and registrationcode_contents.
The registration code can only be enrolled via the API to provide automated smooth workflow to your needs.
For a more detailed insight see the code documentation Registration Code Token.