Why Do I Keep Getting Error 424 for This VBA Sub?

I am trying to create a Sub that takes 3 inputs. The first two inputs have no issues, but the third does not work. I get Error 424 every time I try to call the function, which states that an object is required and highlights the line shown below with asterisks.

Getting this function to work would save a significant amount of time and lines of code since the worksheet will contain a lot of checkboxes. The overall idea is that when the user checks the box and the first input cell number reads "FAIL", the second input cell will have its value changed to contain the username and the date at which it was checked. I am sure that this is a basic fix, but how can I go about fixing it?

Sub Approval(PF, Val, BoxNum)
    If Range(PF).Value = "FAIL" Then
      If BoxNum.Value = True Then
        User = Application.UserName
        Dim Today
        Today = Date
        Range(Val).Value = User & "   " & Today
      Else
        Range(Val).Value = ""
      End If
    Else
        BoxNum.Value = False      **********
        Range(Val).Value = ""
        Exit Sub
    End If
End Sub

Private Sub CheckBox1_Click()
    Call Approval("O28", "R28", "CheckBox1")
End Sub

I tried looking at the Microsoft VBA guide as well as other posts on SO for related content, but none of them seemed like they applied to this. It is also worth mentioning that the code did work before I attempted to turn it into a sub that is called.

Call Approval("O28", "R28", "CheckBox1") passes a string "CheckBox1" to the sub. You probably want to pass the checkbox object.

Try Call Approval("O28", "R28", CheckBox1) - notice no quotes around CheckBox1. Although without seeing the rest of your code, I can't say if this will work.

This is also a good example why it is best practice to specify the type of your arguments like:

Sub Approval(PF as Range, Val as String, BoxNum as Object)

This would help catch the problem earlier and make it easier to identify the issue.

From the looks of your code I think Kevin's answer is the correct one. To expand slightly on Kevin's answer, I would highly recommend that you always have the following line of code at the top of every module:

Option Explicit

This will force you to declare every variable type and as Kevin said, it is best practice. As a big side benefit, it will also detect any variables that may have been spelled incorrectly which can cause no end of issues within your code until you find the spelling error