为什么我在循环时收到错误消息

问：

' the loop statement 
do while messagessent < messages submitted 
    messagessent = messagesent + 1
    Dim client  = New RestClient("https://api.infobip.com/sms/1/text/multi")

    foneno = trim(foneno.Replace(",",""","""))

    Dim request = New RestRequest(Method.POST)
    request.AddHeader("accept", "application/json")
    request.AddHeader("content-type", "application/json")
    request.AddHeader("authorization", "Basic NutrtryoYW5nZW1lMUE=") 'base64   of usename and password
    request.AddParameter("application/json","{""messages"":[{""from"":""" +  senderid + """,""to"":["""& mobileno &""" ],""text"":""" + message + """}]}",ParameterType.RequestBody)

    Dim eresponse As IRestResponse = client.Execute(request)
loop