Validate entry of an input box - validation

Question

Im trying to get an input box to validate the entries a user will make.
i'm using the below script but cant get the validation to work, any help would be appreciated.
Sub inputbox()
Dim Manager As Long
On Error Resume Next
Application.DisplayAlerts = False
Manager = Application.inputbox(Prompt:="Please enter a manager.", Title:="Pick A Manager Name", Type:=1)
On Error GoTo 0
Application.DisplayAlerts = True
If Manager = "" Then
Exit Sub
ElseIf Manager <> Ben, Cameron, Chris, Martin, Peter Then
MsgBox "Incorrect Name, pick a new one!"
Else
MsgBox "Your input was " & Manager
End If
End Sub

Answer 1

Although a Sub name same as built in ones are not recommended, you can do what you are after like below.
First you need to change the InputBox Type to 2 (String), since you are comparing with String. Then you should make a function to check if the input is part of a Manager List.
Sub inputbox()
On Error Resume Next
Dim Manager As String
Manager = Application.inputbox(Prompt:="Please enter a manager name:", Title:="Pick A Manager Name", Type:=2)
If Manager <> "" Then
If IsManager(Manager) Then
MsgBox "Your input was " & Manager
Else
MsgBox "Incorrect Name, pick a new one!"
End If
End If
End Sub
Private Function IsManager(sTxt As String) As Boolean
Dim aManagers As Variant, oItem As Variant, bAns As Boolean
aManagers = Array("Ben", "Cameron", "Chris", "Martin", "Peter")
bAns = False
For Each oItem In aManagers
If LCase(oItem) = LCase(Trim(sTxt)) Then
bAns = True
Exit For
End If
Next
IsManager = bAns
End Function
UPDATE (Improved version suggested by Simon1979):
Private Function IsManager(sTxt As String) As Boolean
On Error Resume Next
Dim aManagers As Variant
aManagers = Array("Ben", "Cameron", "Chris", "Martin", "Peter")
IsManager = Not IsError(Application.WorksheetFunction.Match(Trim(sTxt), aManagers, 0))
End Function

Answer 2

Haven't used the InputBox with Excel but I imagine it will be very similar to the Access one. I use the below method to validate inputbox:
Dim strM as string
EnterManager:
strM = InputBox("Enter Manager.")
If StrPtr(strM) = 0 Then 'Cancel was pressed
' Handle what to do if cancel pressed
Exit Sub
ElseIf Len(strM) = 0 Then 'OK was pressed with nothing entered
MsgBox "You must enter a Manager."
GoTo EnterBuyer
End If
To add your criteria you could add on another If, I'm not sure you can use the approach you have for checking the list of names. Also don't understand how you compare a long Manager with a list of names Ben, Cameron, Chris, Martin, Peter, unless they are assigned variables, in which case I would suggest adding prefixes so it is more obvious such as lBen as opposed to strBen so you can easily see the difference in variable type.
If strM <> "Ben" And strM <> "Cameron" And strM <> "Chris" And strM <> _
"Martin" And strM <> "Peter" Then
MsgBox "Incorrect Name, pick a new one!"
Else
MsgBox "Your input was " & strM
End If