Get-PnPTenantSite : The remote server returned an error: (401) Unauthorized.

When using the `Get-PnPTenantSite` command in PowerShell, an error is encountered, indicating unauthorized access (HTTP error 401).

Step 1: Validate Microsoft 365 License

Verify that the admin user, for whom SharePoint permissions are being enabled, has a valid Microsoft 365 license.

Step 2: Check Site URL Accessibility

1. Ensure that the Site URL, for which permissions are being added, is accessible through a web browser.
2. If not accessible, grant the necessary permissions for the admin user to access the Site URL.

Step 3: Verify DisableCustomAppAuthentication Value

Check the `DisableCustomAppAuthentication` value from the SharePoint Online organization properties for the admin user.

1. Execute the following PowerShell commands:
   

Install-Module Microsoft.Online.SharePoint.PowerShell

Connect-SPOService -Url https://yourtenant-admin.sharepoint.com

1.    In the pop-up window, log in with the admin credentials associated with the SharePoint permissions.
   

Get-SPOTenant

1. If the `DisableCustomAppAuthentication` value is set to `true`, execute the following command to set it to `false`:
   

Set-SPOTenant -DisableCustomAppAuthentication $false

Note: Ensure that you have the necessary permissions to make changes at the SharePoint Online organization level.