Just select any other device that gives you a 7.3 option for a license. It doesn't matter that your license is for a MC70 or MC45, or any device really. All that matters is that you have a license with a platform version for the same version of TE that is installed on your device, and in this case the version is 7.3 (from the website). Be sure to download the client from the wavelink website and not your registration link because if you do select another device then the download link would be for the other type of device in the reg link..
Note that this is an issue with their ordering site and you could open a ticket to have it resolved if you'd like..
Hope this makes sense.