Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello majin123,
Thanks for your post here.
Firstly, I'd like to confirm what kind of Office 365 license you purchased? If you bought Office 365, your product key isn't displayed online. Besides, if you bought Office 365 for Business subscription, you can review your monthly subscription bill in Microsoft 365 admin center > Billing > Bills & Payments. For more information about Office product key, here is an article for your reference: Using product keys with Office.
To better help you, please offer your Office 365 subscription to me for further assistance.
Regards,
Seven