Not passing the right credentials?

[vcuMDD]

I'm having trouble trying to use GMSACredential to connect to a SQL Server with sqlcmd. Here's my current set up:

1. I'm opening powershell with my normal AD account, which has permissions on the SQL server.
2. I'm successfully getting the credential using Get-GMSACredential.
3. I'm using Invoke-GMSACommand to execute a SELECT SUSER_NAME() query on the SQL server.

Expected result: the query will show the gMSA as the account connected to the SQL Server.
Actual result: the query shows my account as account connected to the SQL Server.

Here's my code:

$Cred = Get-GMSACredential -GMSAName 'TheGMSA' -Domain 'TheDomain'
Invoke-GMSACommand -Credential $Cred -ScriptBlock { sqlcmd -E -S TheSQLServer -Q "SELECT SUSER_NAME()" -Y 20 }

Am I misunderstanding the expected usage and the credentials to be passed? Is there a better way to use GMSACredential to run a query on a SQL Server (that we don't control)?

Thanks.