Return an Array from Class Property

Hello All,
I'm in the process of creating a Class (cCampaign) which contains various properties. I've done some simple ones without issue and tested successfully. However, I'm trying to create an additional property that will return an array of Row numbers (generated by searching for the cCampaign object name stored within a Collection Class (called cCampaigns). I've written the code below but it returns a 'Type Mismatch' error. I thought it should be simple to spot but can't see the error in my ways. I would greatly appreciate advice and/or solutions to this problem.
As ever, your patience with my lack of experience is welcomed!

Private pRowNums() As Long

Public Property Get RowNums() As Long
    Dim pplSheet As String
    Dim Campaigns As cCampaigns
    
    pplSheet = "TEST - DO NOT UPDATE (2)"
    
    For Each c In Worksheets(pplSheet).Range("A1:A" & getNextEmptyRow(pplSheet)).Cells
        For i = 1 To Campaigns.Count
            If c.value = Campaigns.Item(i).Name Then
                ReDim Preserve pRowNums(UBound(pRowNums) + 1)
                pRowNums(UBound(pRowNums)) = c.Row
            End If
        Next i
    Next c
    
    RowNums = pRowNums
    
End Property

In the standard module, my intended code will be something like as follows:

    For Each campaign In Campaigns
        For i = 1 To UBound(campaign.RowNums)
            If Range("A" & RowNum(i)) = campaign.Name Then
                X = X + 1
            End If
        Next i
    Next campaign

Thanks for your reply, "shg" - I am now further with my project, but not much.

I've now changed the class properties slightly so that I can return both the full array of row numbers and individual row numbers from the array. To accomplish this I've created a sub that creates the array and simplified the property procedures (and am hoping this is the way to do it). However, when I now run the code I get runtime 91 error (with block not set) at a point that didn't previously stick. I think the issue could be the method or location of the line that calls the sub but i can't be sure. The following extract is within the cCampaigns class that creates a 'cCampaign':

Sub Add(Name As String, Optional Duration As Integer, Optional Rate As Integer, Optional Seats As Integer)
'create a new campaign and add to collection
    Dim c As New cCampaign
    c.Name = Name
    c.Duration = Duration
    c.Rate = Rate
    c.Seats = Seats
    
    Campaigns.Add c
    
    c.assignRowNums
    
End Sub

The assignRowNums code sits within the cCampaign class module and is as follows:

Sub assignRowNums()
    Dim pplSheet As String
    Dim Campaigns As cCampaigns
    Dim c As Range
    
    pplSheet = "TEST - DO NOT UPDATE (2)"
    
    For Each c In Worksheets(pplSheet).Range("A1:A" & getNextEmptyRow(pplSheet)).Cells
        For i = 1 To Campaigns.Count
            If c.value = Campaigns.Item(i).Name Then
                ReDim Preserve pRowNums(UBound(pRowNums) + 1)
                pRowNums(UBound(pRowNums)) = c.Row
            End If
        Next i
    Next c
    
End Sub

Any clues/solutions to why this doesn't work will be much appreciated.