You cannot use a Download Access Code (DAC) directly in the eLicenser software. You must first redeem it to generate the actual 32-character Activation Code. Sign in to your MySteinberg account.
Given that the eLicenser system is permanently shut down, activating a new copy of Cubase 7 is no longer possible. If you have a registered dongle with a working license, you can continue using it. If not, the official upgrade path to a modern Cubase version is your most secure option to continue your musical journey. cubase 7 elicenser activation code link