Get-AzRecoveryServicesBackupItem : Cannot validate argument on parameter 'Container'. The argument is null or empty - azure

Question

I am working on this official tutorial from MS Azure team on Back up a virtual machine in Azure with PowerShell. But while running runbook from Start a backup job section, I get the error shown below. Question: What I may be missing here, and how the issue can be fixed?
Following lines runs fine:
PS C:\Users\myUserName> $vault = Get-AzRecoveryServicesVault -ResourceGroupName "rg-cs-ansible1" -Name "myRecoveryServicesVault"
>> $backupcontainer = Get-AzRecoveryServicesBackupContainer -ContainerType "AzureVM" -Status "Registered" -FriendlyName "myVM" -VaultId $vault.ID
But when I run the following line, I get the error shown below.
PS C:\Users\myUserName> $item = Get-AzRecoveryServicesBackupItem -Container $backupcontainer -WorkloadType AzureVM -VaultId $vault.ID
Error
Get-AzRecoveryServicesBackupItem : Cannot validate argument on parameter 'Container'. The argument is null or empty.
Provide an argument that is not null or empty, and then try the command again.
At line:2 char:16
+ -Container $backupcontainer `
+ ~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidData: (:) [Get-AzRecoveryServicesBackupItem], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.Azure.Commands.RecoveryServices.Backup.Cmdlet
s.GetAzureRmRecoveryServicesBackupItem

Answer 1

Per my test, your commands work fine on my side. I can just reproduce your issue with a wrong VM name this command, even if your VM name is wrong, it will not give an error, but the $backupcontainer will be null, it will cause the error in the next command.
$backupcontainer = Get-AzRecoveryServicesBackupContainer -ContainerType "AzureVM" -Status "Registered" -FriendlyName "myVM" -VaultId $vault.ID
So in your case, please make sure myVM is the correct VM name used for -FriendlyName parameter.