I wanted to follow up to ensure the distinction between internal licensing and commercial hosting licensing was clear, as using the wrong type poses a significant compliance risk. Since you are provisioning Windows Server instances for external clients on your own hardware, the Services Provider License Agreement (SPLA) is the only legally valid framework. Standard Volume Licensing keys found in the Microsoft 365 admin center or retail purchases do not grant hosting rights.
You need to contact an Authorized SPLA Reseller to establish this agreement, which operates on a monthly opex model rather than upfront purchases. Focus your inquiry on Windows Server Datacenter edition licenses for your physical hosts, as this allows you to deploy unlimited guest VMs for your clients without tracking individual instances, simplifying your monthly reporting to the reseller.
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VP