Try this version
Sub GetData_Demo()
    Dim ws As Worksheet, r As Long
    Set ws = ThisWorkbook.Worksheets("Sheet1")
    For r = 1 To ws.Cells(Rows.Count, 1).End(xlUp).Row
        GetData ws.Cells(r, 1).Value, ws.Name, r, 2
    Next r
End Sub


Sub GetData(ByVal sID As String, ByVal wsName As String, ByVal lRow As Long, ByVal lCol As Long)
    Const sURL As String = "https://www.elta-courier.gr/track.php"
    Dim a, http As MSXML2.ServerXMLHTTP60, col As Collection, json As Object, postData As String, sResp As String, i As Long, cnt As Long
    Set http = New MSXML2.ServerXMLHTTP60
    postData = "number=" & sID
    
    With http
sPoint:
        .Open "POST", sURL, False
        .setRequestHeader "User-Agent", "Mozilla/5.0"
        .setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
        .send postData
        .waitForResponse
        sResp = .responseText
        If InStr(sResp, "Fatal error") Then cnt = cnt + 1: Debug.Print "Wait .. " & cnt: GoTo sPoint
    End With
    Set json = JSONConverter.ParseJson(sResp)
    Set col = json("result")(sID)("result")
    ReDim a(1 To col.Count, 1 To 1)
    For i = 1 To col.Count
        a(i, 1) = col.item(i)("status")
    Next i
    ThisWorkbook.Worksheets(wsName).Cells(lRow, lCol).Value = a(2, 1)
End Sub
* I have updated the code as I noticed the site is down sometimes.