Is it possible to install with the same APPIAN SERVER licenses a structure mirro

The license is tied to the OS, Fully Qualified Domain Name and number of CPUs. If the backup is a different server, then the license will not work.

Well, then I have to buy two sets of licenses for my mirror, right?

You will need to discuss that with your Account Executive who can provide you with more detailed information according to the terms of your contract.

Thanks