You solution is to pass it like (,$servicesList)
$session = New-PSSession -ComputerName .
$servicesList = "Service1", "Service2", "Service3"
Invoke-Command -ScriptBlock {
Param ([string[]]$newServicesList)
Write-Host $newServicesList
} -ArgumentList (,$servicesList) -Session $session
Remove-PSSession $session
possible explanation from this SO answer.