There are two versions of the Nurburgring track., Grand Prix Strecke and Nordschleife.
You need both versions to have access to the Combined configuration of Nurburgring.
If you already own one version, please log into iRacing and go to Store...Buy Tracks...Add to Cart the other Nurburgring track you currently don't own. Then follow the rest of the online instructions to complete the transaction.
If you don't own either Grand Prix Strecke or Nordschleife, please add both Grand Prix Strecke and Nordschleife to your cart and checkout to gain access to the Combined configuration.