Hi ___Thomas___88
For your Citrix farm, you need to purchase RDS CAL (Client Access License) and RDSH CAL (Remote Desktop Session Host Access License). RDS CAL allows users to access a remote desktop session host from any device, whereas RDSH CAL allows multiple users to access a remote desktop session host at the same time. You need to purchase the appropriate license for each user or device.
For Windows Server external connectors, you need to purchase and install a Windows Remote Desktop Server external connector license. You will need to purchase one license for each server.
For more information about licensing your RDS deployment with client access licenses (CALs) and activating the remote desktop services license server , please see License your RDS deployment with client access licenses (CALs) | Microsoft Learn and Activate the Remote Desktop Services license server | Microsoft Learn.
Hope it helps,
Lei