Run Command Prompt as administrator:
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Disconnect your PC from the internet. Then open Clean Master 66 and try to enter your license key again. Some versions allow offline activation if the key is hard-coded locally. If it works, block the application in your firewall to prevent it from re-checking the server. Run Command Prompt as administrator: If you want
You can attempt to contact support via their official website. However, be realistic: they no longer actively support legacy PC products. If your key was paid, ask for a migration to a newer product (like Clean Master for Android or a refund). clean master 66 for pc license key fix