(Updated)pasting text from one page into the first empty cell of another page

[Kingman]

Here is a new code snippet that I am trying. Seems to get me closer, but I get an error.

Private Sub Check33_Click()
   
   Dim FirstEmpty As Range
   Sheet6.Activate
   Set FirstEmpty = Cells(Rows.Count, "B").End(xlUp)(2)
      
   If Sheet2.Range("K23").Value = True Then
   ActiveWorkbook.Sheets("Sheet6").Range(FirstEmpty).Value = Sheet2.Range("B23").Value
   End If
    
End Sub

This line gives me a 'Subscript out of range' error

ActiveWorkbook.Sheets("Sheet6").Range(FirstEmpty).Value = Sheet2.Range("B23").Value

One thing I did not mention before, I am trying to paste from merged cells to merged cells. I want the first empty cell in the "B" col on sheet6


Here is what I am trying to do. I have cells with text. There is a cell next to each with a check box. When the checkbox is checked I want the text to be pasted into the first empty cell of a different sheet.
So, the text in cell B3 on Sheet1 is filled in, the checkbox is clicked, the code reads the value in the linked cell, if True then the text is posted to the first empty cell on SheetA(at least, this what I would like to have happen) The code below is what I was able to come up with after searching this forum and with my old knowledge from VB4. I believe I am close since the sheet does get activated when the box is checked. I am able to get it to post to a specified cell by using the code in the second sample, but I have over 100 checkboxes and I don't want a Sub for each one. Hopefully this is clear enough for someone to be able to help me. Thanks

Private Sub Check33_Click()
  Dim lastRow As Long
    ThisWorkbook.Activate
    SheetA.Activate
    'lastrow is the last row without data
    lastRow = ActiveSheet.Cells.SpecialCells(xlCellTypeLastCell).Row + 1
    
    If Sheet2.Range("K23").Value = True Then
       SheetA.Range("lastRow").Value = Sheet2.Range("B23").Value
    End If
End Sub

Private Sub Check79_Click()
    If Sheet3.Range("K13").Value = True Then
       SheetA.Range("B101").Value = Sheet3.Range("B13").Value
    End If
End Sub