The New-MgUser cmdlet is part of the Microsoft Graph PowerShell SDK, which is a module that allows you to interact with the Microsoft Graph API. The Microsoft Graph API is a service that provides access to data and insights across Microsoft 365, such as users, groups, mail, calendar, contacts, files, and more1.
The New-MgUser cmdlet can be used to create new users in your Azure AD tenant, but it has some limitations and requirements. For example, you need to have the Global Administrator or User Administrator role in your tenant, you need to authenticate with the Microsoft Graph API using a certificate or a client secret, and you need to specify the required parameters for the new user, such as userPrincipalName, accountEnabled, displayName, mailNickname, and passwordProfile2.
However, the New-MgUser cmdlet does not support creating guest user accounts in your Azure AD tenant.
Guest user accounts are accounts that belong to external users from other organizations or domains. Guest user accounts have limited access and permissions in your tenant, and they are typically used for collaboration or sharing purposes3.
To create guest user accounts in your Azure AD tenant, you need to use a different cmdlet: New- AzureADMSInvitation. This cmdlet is part of the Azure AD PowerShell module, which is a module that allows you to manage your Azure AD resources and objects. The New-AzureADMSInvitation cmdlet can be used to create and send an invitation email to an external user, which contains a link to join your Azure AD tenant as a guest user. You can also specify some optional parameters for the invitation, such as the invited user display name, message info, redirect URL, or send invitation message.
Therefore, to meet the goal of creating guest user accounts for 500 external users from a CSV file, you need to use a PowerShell script that runs the New-AzureADMSInvitation cmdlet for each user, not the New-MgUser cmdlet.

Change the Service administrator for an Azure subscription
Sign in to Account Center as the Account administrator.
Select a subscription.
On the right side, select Edit subscription details.
Scenario: Designate a new user named Admin1 as the service administrator of the Azure subscription.
References: https://docs.microsoft.com/en-us/azure/billing/billing-add-change-azure-subscription- administrator

Explanation:

Box 1: 6
4 daily + 1 weekly + monthly
Box 2: 8
4 daily + 2 weekly + monthly + yearly