i'm Italian and recently I downloaded the trial version of Flash Professional... when the 30 days ended I was asked to fill in a serial number! And that's the problem: my teacher gave me several serial numbers but they are not valid!
Please, speak Italian if you can! If not no problem! I'm fluent in English too!
Cloud programs do not use serial numbers... you log in to your PAID Cloud account to download & install & activate... you MAY need to log out of the Cloud and restart your computer and log back in to the Cloud for things to work
Some general information for a Cloud subscription
Log out of your Cloud account... Restart your computer... Log in to your paid Cloud account