Loop through column B in multiple worksheets

I am new to VBA and am making a template, in which the user selects upto 20 merchant names. The first merchant name range is called antMerchantNaam, as you can see here: Template

What I want is to loop through column B in every sheet in another workbook which is called wbMerchantBieb in my code. This workbook looks like this:

And I want to retrieve the offset value next to it from column C and column D and store that in the variable strToelichtingMerchant

I have already tried to use the VLookup, but this gives me error '9': Subscript out of range:

Function MerchantsPrefillVol() As String

Dim i, j As Double, dCount As Double, strMerchants As String
Dim strToelichtingMerchant, strUrl As String
Dim wbMerchantBieb As Workbook
Dim wsTemplate, ws As Worksheet

Application.ScreenUpdating = False

Set wsTemplate = ThisWorkbook.Worksheets("Template")
Set wbMerchantBieb = Application.Workbooks.Open(cStrMerchantBieb)

With wsTemplate
'Count merchants
For i = 0 To 20
    If .Range("antMerchantNaam").Offset(0, i).Value <> "" Then
        
        MerchantsPrefillVol = MerchantsPrefillVol & "Merchant " & .Range("antMerchantNaam").Offset(0, i).Value
        
        strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Crypto & Trading").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
        Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Crypto & Trading").Range("B:D"), 3, False)
        
        If IsError(strToelichtingMerchant) Then
            
            strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Moneytransfer").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
            Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Moneytransfer").Range("B:D"), 3, False)
            
            If IsError(strToelichtingMerchant) Then
            
                strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Gambling").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
                Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Gambling").Range("B:D"), 3, False)
                
                If IsError(strToelichtingMerchant) Then
            
                    strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Donation").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
                    Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Donation").Range("B:D"), 3, False)
                
                    If IsError(strToelichtingMerchant) Then
            
                        strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("High Risk Terrorism Activity").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
                        Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("High Risk Terrorism Activity").Range("B:D"), 3, False)
                    
                        If IsError(strToelichtingMerchant) Then
            
                            strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Whitelist").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
                            Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("Whitelist").Range("B:D"), 3, False)
                        
                            If IsError(strToelichtingMerchant) Then
            
                                strToelichtingMerchant = Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("High Risk Terrorism Country").Range("B:C"), 2, False) & Chr(10) & Chr(10) & _
                                Application.VLookup(.Range("antMerchantNaam").Offset(0, i).Value, wbMerchantBieb.Worksheets("High Risk Terrorism Country").Range("B:D"), 3, False)
                            
                                If IsError(strToelichtingMerchant) Then
                                    strToelichtingMerchant = ""
                                End If
                            End If
                        End If
                    End If
                End If
            End If
        End If

        
        If LCase(.Range("antMerchantNaam").Offset(1, i).Value) = "ja" Then
            
            MerchantsPrefillVol = MerchantsPrefillVol & " is opgenomen in de Merchant bibliotheek. Hierin staat het volgende: " & Chr(10) & strToelichtingMerchant & Chr(10) & Chr(10) & .Range("antMerchantNaam").Offset(2, i).Value & Chr(10) & Chr(10)
        Else
            MerchantsPrefillVol = MerchantsPrefillVol & Chr(10)
        End If
        
    End If
Next i

End With
End Function

Maybe try a loop-based approach.

This is untested, but should be pretty close if I've understood your posted code correctly.

Function MerchantsPrefillVol() As String

    Dim i, j As Double, dCount As Double, strMerchants As String
    Dim strToelichtingMerchant, strUrl As String, cStrMerchantBieb
    Dim wbMerchantBieb As Workbook, merch, c As Range
    Dim wsTemplate, ws As Worksheet, arrWsNames, wsName, rngVL As Range, m
    
    'cStrMerchantBieb = "C:\Temp\Test.xlsx"
    
    Application.ScreenUpdating = False
    
    Set wsTemplate = ThisWorkbook.Worksheets("Template")
    Set wbMerchantBieb = Application.Workbooks.Open(cStrMerchantBieb)
    
    arrWsNames = Array("Crypto & Trading", "Moneytransfer", "Gambling", _
                       "Donation", "High Risk Terrorism Activity", _
                       "Whitelist", "High Risk Terrorism Country")
    
    For Each c In wsTemplate.Range("antMerchantNaam").Resize(1, 20).Cells
        merch = c.Value
        If Len(merch) > 0 Then
            MerchantsPrefillVol = MerchantsPrefillVol & "Merchant " & merch
            
            If LCase(c.Offset(1).Value) = "ja" Then
                strToelichtingMerchant = ""
                For Each wsName In arrWsNames
                    Set rngVL = wbMerchantBieb.Worksheets(wsName).Columns("B") 'lookup column
                    m = Application.Match(merch, rngVL, 0) 'look for match
                    If Not IsError(m) Then                 'got match?
                        strToelichtingMerchant = rngVL.Cells(m).Offset(0,1).Value & vbLf & vbLf & _
                                                 rngVL.Cells(m).Offset(0,2).Value
                        Exit For
                    End If
                Next wsName
                MerchantsPrefillVol = MerchantsPrefillVol & _
                    " is opgenomen in de Merchant bibliotheek. Hierin staat het volgende: " & _
                    Chr(10) & strToelichtingMerchant & Chr(10) & Chr(10) & _
                    c.Offset(2).Value & Chr(10) & Chr(10)
            Else
                MerchantsPrefillVol = MerchantsPrefillVol & Chr(10)
            End If
            
            
        End If
    Next c
End Function