Issues to switch Parallels 17 from a Mac to another Mac

Hey guys, so I'm here to ask for some help. My father gave me his parallels account, which was installed on his macbook air. I am now trying to install it on my iMac. The license is for Parallels 17. I was able to download it and to insert the license but in the end, once it takes the credentials and the license conde, it gives me this error: "Impossibile verificare la firma di licenza". Which means impossible to verify the sign of license. I ve done the access to the official site but I can't see any other laptop connected to it. He confirmed to have uninstalled correctly the older application from his own laptop. Now I can't really be in touch with any assistent, no numbers to phone, no emails...here's a very big trouble since I was planning to use this program to work these days. Is there any way possible you could help me?