RDS CALs are forward-compatible, meaning a 2022 or 2025 license has the legal right to cover an older 2012 R2 server.
The most reliable way to license a Windows Server 2012 terminal server today is to purchase the of RDS CALs and use downgrade rights . buy terminal server licenses 2012
For legitimate licensing, you should look for authorized Microsoft Licensing Partners or reputable resellers: Windows Server 2012 R2 - Microsoft Lifecycle RDS CALs are forward-compatible, meaning a 2022 or