If you’ve decided to activate your copy of CleanMyMac 3, please be sure you have the Activation Number nearby. If you don't have it, you can purchase the CleanMyMac 3 license at the MacPaw store and the number will be sent to your email immediately after purchase.
When you attempt to activate CleanMyMac 3 with your Activation Number, CleanMyMac 3 will establish a connection with the MacPaw server, which then checks whether the entered Activation Number is valid or not.
However, if you have the built-in, OS X firewall enabled, CleanMyMac 3 will be unable to establish this connection. Below is a set of short instructions on how to disable the firewall for CleanMyMac 3 Activation.
1. Open System Preferences.
2. Click on the Security & Privacy icon in the Personal section.
3. Open the Firewall tab.
4. Click Turn Off Firewall in the newly opened window to disable the firewall.
Note: You may be required to click the lock icon and type in your password to enable this feature.
5. Open CleanMyMac 3 and re-enter your Activation Number.
6. After successfully activating CleanMyMac 3, go back to the Security window and click Turn On Firewall.
That's all there is to it!