barcode scan and save into file

There is no lostfocus event for textboxes in VBA.

When you double_click a control, the Editor will automatically insert a default event. While the cursor is inside this event, you can choose from a list of available events in the upper right dropdown. (You can also choose the control from the left dropdown,)

Private Sub txtBarcode_Exit(ByVal Cancel As MSForms.ReturnBoolean)
Dim WS As Worksheet
Dim NextRow As Long

    Select Case Len(Me.txtBarcode.Text)

    Case 12
        Set WS = Worksheets("Barcode_Data")
        With WS
            NextRow = .Cells(.Rows.Count, "A").End(xlUp).Row + 1

            Range("A" & NextRow) = txtseqnum.Value
            Range("B" & NextRow) = txtBarcode.Value
        End With
        txtseqnum.Value = ""
        txtBarcode.Value = ""

    Case Else
        MsgBox "Barcode incorrect", vbInformation, "Barcode scan"
        Me.txtBarcode.SetFocus
        Cancel = True
    End Select
End Sub

Private Sub txtseqnum_Exit(ByVal Cancel As MSForms.ReturnBoolean)
    If Len(Me.txtseqnum) <> 7 Then
        MsgBox "Seqyunce number incorrect", vbInformation, "Sequence number"
        Me.txtseqnum.SetFocus
        Cancel = True
    End If
End Sub