To manage Chrome devices across your organisation, you need a license for each device you want to manage. The license gives you access to device settings in the Google Admin console. You need a license to enroll a device. If you don’t have one, you’ll see an error. You then have to purchase a new license, or deprovision an enrolled device to make its license available.
Chrome device management license
A Chrome device management license is used to configure settings and enforce policies for a specific Chrome device. It gives you access to device settings that let you control user access, customize features, configure network access, and more. You can purchase this license for the life of the device.