Someone from eleven forums said this 365 Office forum subgroup might help me with my questions.

I bought a 365 Personal plan 12 month sub with Product key in shrink wrapped box from a big box retailer. I opened the box. Big mistake maybe before finding out more. I have a Win 11 PC with 12 month 365 Basic plan. If I follow the instructions it will ask me for my current Microsoft account email address. First, it is not @Outlook.com, ok? Second after I enter the 365 Personal Plan product key from the box will it automatically switch my account Plan to Personal? What happens when it renews? What happens when I hit the Manage plan button on my pc? I just read somewhere it sends me back to the big box retailer where I am sure they'll just send me back to Microsoft. Is That correct? Do I get any tech support from Microsoft?

I'll be glad if you can provide the answers to me before I use that key?

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I finally got in touch with Microsoft 365 support. When I activate the sub it gets linked to my existing Microsoft account email I specify whether or not it's an outlook.com address. In any case the billing and plan management gets linked to the account email used at activation. In any case they will tech support it. Also, with product key from valid 3rd party retailer everything gets attached to Microsoft account used to activate it.

In case anybody else does not know.