A usage-medium is the medium that is being used by the end-user to conduct a session. “Session” in this case can be a charging-session but also the usage of a car-sharing vehicle or other rentable objects.
Concrete usage-mediums in Gridware are:

E-Mobility Native App for contract-users
in the style of the EMP in question

RFID-Karte or dongle for contract-users
in the style of the EMP in question

RFID Admin Card or Dongle for facility managers
authorized everywhere

Web-App for spontanous users
Entering usually via QR-Code Sticker (instead of publishing on a roaming platform)

ISO 15118 vehicle for contract-users or roaming-users
can authorize themselves via E-Mobility Account Identifier (EMAID)

Third-party app for roaming-users
obviously only for publicized charging stations

Third-party EMP RFID card for roaming-users.
obviously only for publicized charging stations

Third-party apps for contract-users
Connection directly with the Gridware API, valid for freely defineable charging stations.