This information applies to all versions
There are multiple reasons that could cause this issue.
Are the system time (date & clock), time zone, and location of your computer correct? Are all toggles set to "automatic?"
Is there an antivirus, firewall, proxy, or similar tool that could be blocking the activation? If so, please try temporarily disabling it and see if the activation is then successful.
Otherwise, please open a ticket with customer support and include the exact text of the error message you are receiving.
Please click this link to request help from the DxO Support Team.
Note: screenshots are extremely helpful and allow us to see what's on your screen. Please attach one to your ticket.