Newly bought Parallels 15, installing it on new Mac while account and old versions are on old Mac

On my old Mac I used different versions of Parallels (visible in my account under "legacy licenses"). Now I've bought a new Mac and also the latest version of Parallels (15). When I try to activate it with the new key it says "already in use" -> I choose "Activate on this Mac" -> but then "not possible". I've even signed out on the old Mac (where I never had installed a version later than 11 and surely not version 15). Please help. Of course I can send you the purchase receipt with the activation key (just tell me where to send to).

 

Hi MartinL18, thank you for reaching out! We have sent you a private message, please reply to us back there so that we could check and help you better. Thanks, Saravanan.