Does anyone know what the procedure for getting the Delta Medallion discount and points credit applied to a Sixt rental are? On the Delta website, it says the promotion is as follows:

Sixt rent a car
Earn 500 miles per car rental.
Earn 1000 miles per chauffeur service.
Up to 10% discount* for all SkyMiles members.
Up to 15% discount* for Gold or Platinum Medallion members.

*Applied to all online and offline rates.

However, doing a dummy booking through the normal Sixt.com site or by clicking on the link from Delta yields the same prices. Is there something I'm missing here?