VBA functions & Arguments

Ok, so I am about to finalize my work and need help with the final step.

So far I have 2 Function with a sub to test

Private Sub test_getBaristaSalary()
Dim InputYear As Integer

    InputYear = InputBox(Prompt:="How many years of Experience?")
    MsgBox Prompt:="Total Salary is $" & getBaristaSalary(Whatyearisit:=InputYear)

End Sub

Function getBaristaSalary(Whatyearisit As Integer)

  
    getBaristaSalary = Whatyearisit * 500 + 18000
    ' Annual Salary = $18000 + $500x(years as barista)
End Function

Function 2 is

Private Sub test_getManagerSalary()
Dim InputYearBarista As Integer
Dim InputYearManager As Integer

    InputYearBarista = InputBox(Prompt:="Years of experience as Barista?")
    InputYearManager = InputBox(Prompt:="Years of experience as Manager?")
    MsgBox Prompt:="Total Salary is $" & getManagerSalary(BaristaYear:=InputYearBarista, ManagerYear:=InputYearManager)

End Sub

Function getManagerSalary(BaristaYear As Integer, ManagerYear As Integer)
  
    getManagerSalary = (BaristaYear * 500) + (ManagerYear * 1000) + 22000
    ' Annual Salary = $22000 + $500x(years as barista) + $1000x(years as a manager)
End Function

My third function needs to determine which of the first 2 functions will be used to calculate the equation based on the answer to InputYearManager. If the value of InputYearManager is anything besides 0 then I need to use the second function however if 0 is the answer then I need the first function used.

So far I have this:
[B]

Private Sub test_getPredictedSalary()
Dim InputYearBarista As Integer
Dim InputYearManager As Integer

    InputYearManager = InputBox(Prompt:="Years of experience as Manager?")
    InputYearBarista = InputBox(Prompt:="Years of experience as Barista?")
    MsgBox Prompt:="Total Salary is $" & getPredictedSalary(BaristaYear:=InputYearBarista, ManagerYear:=InputYearManager)
End Sub

Function getPredictedSalary(BaristaYear As Integer, ManagerYear As Integer) As Double

If InputYearManager >= 0 Then
    getPredictedSalary = getManagerSalary
ElseIf InputYearManager = 0 Then
    getPredictedSalary = getBaristaSalary

End If
End Function


' Annual Salary = $22000 + $500x(years as barista) + $1000x(years as a manager)
' Annual Salary = $18000 + $500x(years as barista)

When I run this I get a Complie Error: Argument not optional. Any suggestions?