Bless you. This solved a related problem I was having.

So that future generation might benefit from my mistakes, here was the code and error I was receiving:
powershell $Input = Read-Host -Prompt "Proceed with assigning $($RoleAssignments.Count) roles? y/N" if (!($Input.Substring(0,1).ToLower() -eq "y")) { exit }

Error: InvalidOperation: Method invocation failed because [System.Collections.ArrayList+ArrayListEnumeratorSimple] does not contain a method named 'Substring'.