Invoke-Command error "Parameter set cannot be resolved using the specified named parameters"

The error you have is because -credential without -computername can't exist.

You can try this way:

Invoke-Command -Credential $migratorCreds  -ScriptBlock ${function:Get-LocalUsers} -ArgumentList $xmlPRE,$migratorCreds -computername YOURCOMPUTERNAME

The accepted answer is correct regarding the Invoke-Command cmdlet, but more broadly speaking, cmdlets can have parameter sets where groups of input parameters are defined, such that you can't use two parameters that aren't members of the same parameter set.

If you're running into this error with any other cmdlet, look up its Microsoft documentation, and see if the the top of the page has distinct sets of parameters listed. For example, the documentation for Set-AzureDeployment defines three sets at the top of the page.