Need Help with MGGraph Calendar Permissions – Getting Access Denied

I'm having some trouble with granting calendar permissions on a room mailbox using Microsoft Graph. The client needs everyone to be able to edit the calendar, which I'd normally handle easily with MSOnline. However, I'm hitting an 'Access Denied' error even though I believe I have all the right scopes. I'm logged in as the global admin, and I've already consented to the necessary permissions for my organization. Here's the code snippet I'm working with for context:

```
$UserID = Read-Host -Prompt 'Enter Target Mailbox Email'
Connect-MgGraph -Scopes "Application.ReadWrite.All", "AppRoleAssignment.ReadWrite.All", "RoleManagement.ReadWrite.Directory", "Calendars.ReadWrite"
$Calendar = Get-MgUserCalendar -UserId $UserId | Where-Object { $_.IsDefaultCalendar -eq $true }
$CalendarId = $Calendar.Id
$Permissions = Get-MgUserCalendarPermission -UserId $UserId -CalendarId $CalendarId
$DefaultPermission = $Permissions | Where-Object { $_.EmailAddress.Name -eq "My Organization" }
$CalendarPermissionId = $DefaultPermission.Id
$Params = @{ Role = "Write" }
Update-MgUserCalendarPermission -UserId $UserId -CalendarId $CalendarId -CalendarPermissionId $CalendarPermissionId -BodyParameter $Params
$UpdatedPermissions = Get-MgUserCalendarPermission -UserId $UserId -CalendarId $CalendarId
$UpdatedPermissions | Where-Object { $_.EmailAddress.Name -eq "My Organization" } | Select-Object Role
Disconnect-MgGraph
```

The first 'Access Denied' comes from the `Get-MgUserCalendarPermission` command. I'd appreciate any advice on how to resolve this! Thanks a lot!