One of the simple solutions I like most is to distribute a license file after purchase. The license can be a JWT or an X509 cert or something else with a signat

One of the simple solutions I like most is to distribute a license file after purchase. The license can be a JWT or an X509 cert or something else with a signature you can verify offline in the app. It will not prevent multiple use without phoning home but I don't think it's that much of an issue. Pirates are not going to pay for your software anyway.