Generic Key to Install:
If you don't have a license to install Server 2025, you can use a Generic key to install, but it is only for installation, not for activation. 
Windows Server 2025 Standard Key: MFY9F-XBN2F-TYFMP-CCV49-RMYVH
Windows Server 2025 Datacenter Key: 2KNJJ-33Y9H-2GXGX-KMQWH-G6H67