The one that i got once i ve already used it and it doesn t work anymore.
Please help me!!!
Welcome to the forum.
The code you’ve got is a one time code and not working anymore.
To know how to activate your license you need to tell us what exact version and edition of Cubase you want to activate.
Cubase LE 12 for windows, i bought a a Fluid audio SRI-2 USB interface and it was included there. Where i can find the specifications you need?
Cubas 12 LE relies on the new Steinberg Licensing, so all you need to do is to install the software on your machine, via the Download Assistant. This will also install the Activation Manager which is needed for the Licensing.
When everything is installed start the Activation Manager, log in to Steinberg using your mySteinberg account (the same you are using here in the forum) and then you can press the Activate button to make it work.
Here is a description for all of that
It appears "valid license not found. 
i have the same issue with a UR22 interface. i have cubase 8