ShowAllData method of Worksheet class failed

wish helps you I don't know what GWP is, but I think you want to use ProjNo there. The Range property doesn't accept an argument like that. Unless you have a named range of "Row,6" which you don't because it's not a legal name, you have to supply Range with a valid range reference, like A6 or D2:D12, for example.
Also, you can't concatenate rows and use them in a Range reference to get a larger range. You would have to copy each row inside the loop, union the ranges as you go, or better yet, filter on the value that you want and copy the visible rows.

Private Sub btnNext_Click()

    With ThisWorkbook.Worksheets("Sheet7")
        'filter for the project id
        .Range("A1", .Cells(.Rows.Count, 1).End(xlUp)).Resize(, 6).AutoFilter 1, "=" & .Range("D6").Value

        'copy the visible rows
        .Range("F2", .Cells(.Rows.Count, 6).End(xlUp)).SpecialCells(xlCellTypeVisible).Copy _
            ThisWorkbook.Worksheets("Sheet1").Cells(19, 5)

        'get rid of the filter
        .AutoFilterMode = False

    End With

End Sub

should help you out I have automated a proper record input into the table that I use as a database, and when the table is filtered the input don't work. , Here is the working solution I went with :

Public Sub UnFilter_DB()
Dim ActiveS As String, CurrScreenUpdate As Boolean

CurrScreenUpdate = Application.ScreenUpdating
Application.ScreenUpdating = False
ActiveS = ActiveSheet.Name

    Sheets("DB").Activate
    Sheets("DB").Range("A1").Activate
    On Error Resume Next
    If Sheets("DB").FilterMode = True Then Sheets("DB").ShowAllData
    On Error GoTo 0

    DoEvents
    Sheets(ActiveS).Activate

Application.ScreenUpdating = CurrScreenUpdate
End Sub

Private Sub TEST_UnFilter_Table()
    Dim tB As Workbook, _
        Sh As Worksheet

    Set tB = ThisWorkbook
    Set Sh = tB.Sheets("DB")

    Call UnFilter_Table(Sh, "Db_Val")
End Sub

Public Function UnFilter_Table(ByRef SheetWithTable As Worksheet, ByVal RangeName As String) As Boolean

On Error GoTo ErrHdlr
    Dim aWB As Workbook, _
        ActiveSH As Worksheet, _
        ScreenUpdateState As Boolean, _
        StatusBarState As Boolean, _
        CalcState As XlCalculation, _
        EventsState As Boolean, _
        DisplayPageBreakState As Boolean

    Set aWB = ActiveWorkbook
    Set ActiveSH = aWB.ActiveSheet

    DisplayPageBreakState = ActiveSH.DisplayPageBreaks
    ActiveSH.DisplayPageBreaks = False

    With Application
        ScreenUpdateState = .ScreenUpdating
        StatusBarState = .DisplayStatusBar
        CalcState = .Calculation
        EventsState = .EnableEvents

        .ScreenUpdating = False
        .DisplayStatusBar = False
        .Calculation = xlCalculationManual
        .EnableEvents = False
    End With


    SheetWithTable.Activate
    SheetWithTable.Range(RangeName).Cells(1, 1).Activate
On Error GoTo 0

On Error Resume Next
    If SheetWithTable.FilterMode Then SheetWithTable.ShowAllData
On Error GoTo 0

On Error GoTo ErrHdlr
    DoEvents
    ActiveSH.Activate
    ActiveSH.DisplayPageBreaks = DisplayPageBreakState

    With Application
        .ScreenUpdating = ScreenUpdateState
        .DisplayStatusBar = StatusBarState
        .Calculation = CalcState
        .EnableEvents = EventsState
    End With

    UnFilter_Table = True
On Error GoTo 0

Exit Function
ErrHdlr:
UnFilter_Table = False
Debug.Print "Error in unfiltering sheet " & SheetWithTable.Name & " !" & vbCrLf & _
            "Error n° " & Err.Number & vbCrLf & _
            Err.Description
End Function

like below fixes the issue It depends of the state of FilterMode.
Personally, I made this (user won't see anything happening) to cancel filters on a sheet :

Public Sub UnFilter_Tables_On_Sheet(Sheet_Name As String)
Dim ActiveS As String, CurrScreenUpdate As Boolean

CurrScreenUpdate = Application.ScreenUpdating
Application.ScreenUpdating = False
ActiveS = ActiveSheet.Name

    Sheets(Sheet_Name).Activate
    Sheets(Sheet_Name).Range("A1").Activate
    On Error Resume Next
    If Sheets(Sheet_Name).FilterMode = True Then Sheets(Sheet_Name).ShowAllData
    On Error GoTo 0

    DoEvents
    Sheets(ActiveS).Activate

Application.ScreenUpdating = CurrScreenUpdate
End Sub

To fix this issue Name, Index and CodeName are three properties of a worksheet, which are quite different. In the code from the screenshot, Sheet21 is a CodeName and it probably corresponds to Worksheets(17).
Worksheet CodeName Property Refer to sheet using codename

Sub TestMe()
    Dim i As Long
    For i = 1 To Worksheets.Count
        Debug.Print Worksheets(i).Name
        Debug.Print Worksheets(i).Index
        Debug.Print Worksheets(i).CodeName
        Debug.Print "-----------------------"
    Next i
End Sub

this will help Solution 1:
Instead of Sheets.("Discount").Activate write Sheets("Discount").Activate and it should work. E.g., remove the dot.