Invoke-sqlcmd using a Connection String with Secrets

Product: PowerShell Universal
Version: 5.6.4

I built out a Connection String that references a number of Secrets, and am passing that into an Invoke-sqlcmd, eg:

Invoke-Sqlcmd -Query $Query -ConnectionString $ConnectionString -As DataSet

The odd thing is my API reports back that auth to the SQL server failed for the user the PSU Service is running as:

Login failed for user ‘DOMAIN\ServiceUser’.
at Invoke-SqlQuery, : line 30

It’s like it ignored the User ID & Password sections of my Connection String. I checked the SQL Server to see, and sure enough… it’s attempting the PSU Service account as the User instead of the one in the CS. Why would the catch list the PSU Service user, and not the one parsed from the CS?

The user/pass are stored as a Secret PSCred, and I reference it in the ConnectionString like:

Password=$($Secret:SQLUSER.Password)

Thanks!