He should be able to configure the computer with his Microsoft account without any charge if he has a Microsoft account. With Windows 10, he can also set it up using a local account that doesn't even need a network connection to work. During initial setup after a factory reset, he should get prompted for this information. What may be requesting a subscription is an factory-installed Microsoft 365 suite, but even if that's the case, there's no requirement to subscribe at that time.
Describe exactly what he's doing and what happens when he does it.