Hello. I am writing this using Google Translate. I was using Parallels Desktop 16 without any issues, but today the activation suddenly expired, and a pop-up appears saying, "<You have entered an upgrade key. Please verify with a key from a previous version.>" Even when I enter keys for Parallels Desktop versions 6 through 11, 13, or 15 registered to my account, the message "<The license server did not accept the previous activation key. Please verify that you have entered the key correctly. Activation keys are stored in your Parallels account. If you do not want to worry about many activation keys and upgrade procedures in the future, we recommend purchasing a Parallels Desktop subscription.>" Please check the attached photo. Thank you.
