B4J Question I cann't use Sleep(1)

Sub Process_Globals
    Private srvr As Server
    Private timer1 As Timer
End Sub

Sub AppStart (Args() As String)
    plc.Initialize
    '
    srvr.Initialize("srvr")
    srvr.Port = 8010
    srvr.AddHandler("/put", "PutHandler", False)
    srvr.AddHandler("/get", "GetHandler", False)
    srvr.Start
    Log($"Server started by ${srvr.Port}"$)
   
    timer1.Initialize("timer1",250)
    timer1.Enabled=True
    StartMessageLoop
End Sub