AirServer licenses are platform-specific. A Mac license can only activate AirServer on Mac computers. A PC license can only activate AirServer on Windows computers.
If you have accidentally purchased the incorrect type of license, and you have not yet activated that license, you can switch it to the opposite platform. However, if you have already activated the license on one platform, you will no longer be able to switch that license to the opposite platform.
If you have not activated the license, find your purchase confirmation email and click the link to manage your activations. If you have no activations on your account, you will find an option to switch your license to the opposite platform. If you have an activation from a previous trial version, just send us an email (firstname.lastname@example.org) with the activation code and ask us to help you.