VBA from latest file in a folder ("Run-time error 1004") - excel

Question

I used the below code to open the latest file in a folder and Vlookup from it and return the value which is in column I.
I am facing a Run-time error 1004, although everything is correct.
i Set wbname = ActiveWorkbook.Name to catch the open sheet name which I will put the Vlookup formula in and I am choosing the correct range for my formula which is I2, still can't figure out where did I go wrong.
Error Message in the below line:
Range("I2").Formula = _
"=VLOOKUP(A2,[" & MyPath & LatestFile & "]'Sheetname with input data'!A:I,9,False)"
My Code:
Sub PrepareforOutlookMails()
wbname = ActiveWorkbook.Name
Dim MyPath As String
Dim MyFile As String
Dim LatestFile As String
Dim LatestDate As Date
Dim LMD As Date
Dim wb As Workbook
Dim fileLocation As String
Dim fileToOpen As Workbook
MyPath = "C:\1.ER\1.Work\19.Etr\Recon\2022\October"
If Right(MyPath, 1) <> "\" Then MyPath = MyPath & "\"
'first Excel file from the folder
MyFile = Dir(MyPath & "*.xls", vbNormal)
'If no files exit the sub
If Len(MyFile) = 0 Then
MsgBox "No files were found...", vbExclamation
Exit Sub
End If
'Loop through each Excel file in the folder
Do While Len(MyFile) > 0
LMD = FileDateTime(MyPath & MyFile)
If LMD > LatestDate Then
LatestFile = MyFile
LatestDate = LMD
End If
MyFile = Dir
Loop
Workbooks.Open MyPath & LatestFile
Workbooks(wbname).Activate
Range("I2").Formula = _
"=VLOOKUP(A2,[" & MyPath & LatestFile & "]'Sheetname with input data'!A:I,9,False)"

Answer 1

Like I mentioned VLOOKUP works on closed file as well. There is no need to open the file.
Your [ and ] and ' placement is incorrect. Here is an example (Untested)
If you manualy type the formula, it will look like this
=VLOOKUP(D2,'C:\1.ER\1.Work\19.Etr\Recon\2022\October\[Mail Merge (Updated Sample File) (1).xlsx]Sheetname with input data'!A:I,9,0)
Sub Sample()
Dim MyPath As String
Dim LatestFile As String
MyPath = "C:\1.ER\1.Work\19.Etr\Recon\2022\October\"
LatestFile = "Mail Merge (Updated Sample File) (1).xlsx"
Range("I2").Formula = "=VLOOKUP(A2,'" & _
MyPath & _
"[" & _
LatestFile & _
"]Sheetname with input data'!A:I,9,0)"
End Sub
EDIT
This is how your original code can be written. I have commented the code so you should not have any problem understanding it.
Option Explicit
Sub PrepareforOutlookMails()
Dim wbThis As Workbook
Dim wsThis As Worksheet
Dim MyPath As String
Dim MyFile As String
Dim LMD As Date
Dim LatestFile As String
Dim LatestDate As Date
Set wbThis = ThisWorkbook
'~~> Change this to the relevant sheet
'~~> This is where the formula will be written
Set wsThis = wbThis.Sheets("Sheet1")
'MyPath = "C:\1.ER\1.Work\19.Etr\Recon\2022\October"
MyPath = "C:\Users\routs\Desktop"
If Right(MyPath, 1) <> "\" Then MyPath = MyPath & "\"
'~~> First Excel file from the folder
MyFile = Dir(MyPath & "*.xls*", vbNormal)
'~~> If no files exit the sub
If Len(MyFile) = 0 Then
MsgBox "No files were found...", vbExclamation
Exit Sub
End If
'Loop through each Excel file in the folder
Do While Len(MyFile) > 0
LMD = FileDateTime(MyPath & MyFile)
If LMD > LatestDate Then
LatestFile = MyFile
LatestDate = LMD
End If
MyFile = Dir
Loop
wsThis.Range("I2").Formula = "=VLOOKUP('" & wsThis.Name & "'!A2,'" & _
MyPath & _
"[" & _
LatestFile & _
"]Sheetname with input data'!A:I,9,0)"
End Sub
Screenshot