Credential Parameter not working for Invoke-sqlcmd - powershell

Question

I am using the Invoke-sqlcmd cmdlet in Powershell to run an SQL query saved in a string against a remote server.
I have included the credential parameter to ask for domain credentials to connect to the SQL instance.
I've tested this without the credential parameter; instead running the Powershell window as the user, this works fine, so I am confident that permissions for the user are set correctly.
However, I cannot get it to work with the credential parameter.
Import-Module -Name SqlServer -force
function Correct-Servername {
param(
[string] $dataSource = ".\SQL",
[string] $database = "MASTER",
[string] $sqlCommand = "sp_dropserver ##servername DECLARE #ServerName SQL_VARIANT = (SELECT serverproperty('Servername')), #SQLQuery NVARCHAR(4000); SET #SQLQuery = 'sp_addserver ''' + CONVERT(NVARCHAR(100), #SERVERNAME) + ''', ''LOCAL''' PRINT #SQLQuery EXECUTE sp_executesql #SQLQuery"
)
$cred = Get-Credential
Invoke-Sqlcmd -Query $sqlCommand -ServerInstance $dataSource -Database $database -Credential $cred
}
Correct-Servername | out-file -FilePath C:\Temp\correct_servername.log
This is the error i receive:
cmdlet Get-Credential at command pipeline position 1
Supply values for the following parameters:
Credential
Invoke-Sqlcmd : Login failed for user 'domain\user'.
At C:\Temp\Rename-Create-Replication-2.ps1:20 char:2
+ Invoke-Sqlcmd -Query $sqlCommand -ServerInstance $dataSource -Dat ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [Invoke-Sqlcmd], SqlException
+ FullyQualifiedErrorId : SqlExceptionError,Microsoft.SqlServer.Management.PowerShell.GetScriptCommand
Invoke-Sqlcmd :
At C:\Temp\Rename-Create-Replication-2.ps1:20 char:2
+ Invoke-Sqlcmd -Query $sqlCommand -ServerInstance $dataSource -Dat ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : ParserError: (:) [Invoke-Sqlcmd], ParserException
+ FullyQualifiedErrorId : ExecutionFailureException,Microsoft.SqlServer.Management.PowerShell.GetScriptCommand
Any assistance is appreciated.