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The McAfee activation problems are too common and frequent to occur; to resolve them, you may need to reset your account. Also, check your product key before submitting the credentials. You need to ensure that the product key is valid and not in use. Just check these normal things and complete McAfee antivirus troubleshooting.

For more info:
https://contactforhelp.com/mcafee/
https://contactforhelp.com/blog/basic-methods-of-resolving-mcafee-antivirus-issues/