File Upload using SharePoint REST API

i have tried to Upload file in SharePoint List.But server returns 400 BAd request error

url:_spPageContextInfo.webServerRelativeUrl+"/_api/web/lists/GetByTitle('"+listName+"')/items("+id+")/AttachmentFiles/add(FileName='" + file.name + "')", method: "POST", binaryStringRequestBody: true, body: binary, success: fsucc, error: ferr, state: "Update"

i have checked the file size.its in KB only.i cant guess where its going wrong

Can anyone help me to resolve this bad request error