My license for Premium is valid until April 2027, activation itself works. However, then, a dialog pops up telling me that my license has expired.
How to fix this?
We do not have access to accounts/billing/licencing here, this is a user forum.
You will need to contact support for licencing and account issues.
You can raise a support ticket by using the form here: CCleaner Support Community
However you should note that support are slow to answer these days and it can take a week or more for a registered customer to get a reply.
Further you should note that the automatic support queue works off email addresses.
So if the email you use when sending the form is not showing as registered to a valid licence then you may not be seen as someone who has (currently) paid for support.
As an apparent ‘non-payer request’ your request will be non-priority and it may be a very long time (month or more) before the system even shows your request to a support person.