Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Which type of account are you trying to use? Note that organization (business) accounts won't be accepted when used with a so-called non-qualifying plan.
For more, see the article at https://support.microsoft.com/en-us/microsoft-365-activation-licensing/mobile/what-you-can-do-in-the-microsoft-365-apps-on-mobile-devices-with-a-microsoft-365-subscription . The screen shot below is from the article.