I purchased a copy of CC Pro in 2019, after using earlier free versions at home for years. Lately, when I try to use CC, it opens with a license prompt, even though I had registered the key in 2019. When I enter the key, an error message says it is invalid. I thought that the purchase was a one-time. Is that license only good for a specified period?
CCleaner Pro licences are usually valid for 1 or 2 years, but can be for longer depending on just what you purchased, special offers, etc.
See: https://support.piriform.com/hc/en-us/articles/204044434-How-long-is-my-license-valid-for-