Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Something important to keep in mind:
Every app and service that you buy directly from Microsoft, including your subscription to Microsoft 365, is not purchased by you - it's purchased by your Microsoft account. You do not own a subscription to Microsoft 365 ... Your Microsoft account owns the subscription, not you and not your computer. You own your computer and you own your Microsoft account, but your Microsoft account owns the subscription. Your Microsoft account pays for a subscription with the method of payment that you provided to your Microsoft account. No other method of payment pays for your subscription.
Therefore, your subscription to Microsoft 365 belongs to the Microsoft account that paid for the subscription with the payment method you entered to that Microsoft account.
In order for you to use the software, after you have downloaded and installed it to your computer with your Microsoft account, you have to activate the software with the username and password of that Microsoft account - no other username and password will activate the software.
To enter the username and password, open any Microsoft 365 app and go to File > Account > User Information and enter the username and password of the correct Microsoft account. Your software will activate and you can use it.