Argument not specified for parameter

Hello
Wrote a short script:

Public Function CCC_MyScriptName(ByVal uidPerson As String) As String
    Dim dbPerson As IEntity = Session.Source.Get("Person", uidPerson)
    Dim Mail As String = dbPerson.GetValue("DefaultEmailAddress").String.ToLower
    Return Mail
End Function

Created a process with a step ScriptComponent - ScriptExec, with parameters:

ScriptName Value = CCC_MyScriptName

 ParameterValue0  Value = $UID_Person$

When compiling the process, I get an error:

Argument not specified for parameter 'uidPerson'.

How do I correctly pass a parameter to a script from a process step?