Changing .Value To.MB

I am running the following query but I'm not able to convert the value to MB
,@{Label="Test";Expression={$_.ProhibitSendQuota.Value.ToMB()}}

Not sure what I'm doing wrong, the attribute is empty:

(Get-MailboxStatistics -server "Mail01-NY" | Where {(!($_.StorageLimitStatus -match "BelowLimit|NoChecki
ng"))} | Select-Object DisplayName -ExpandProperty DisplayName) | Get-Mailbox | Select-Object DisplayName,Alias,ServerNa
me,UseDatabaseQuotaDefaults,IssueWarningQuota,@{Label="Test";Expression={$_.ProhibitSendQuota.Value.ToMB()}}