Unable to create domain Record "API Error: Name can not be just a TLD"

I want to create sub-domains using NodeJS. I used the following Node.JS script but while I ran it I got the above error.

const express = require("express");
const router = express.Router();

var DigitalOceanAPI = require('doapi');
var api = new DigitalOceanAPI({token: 'my_token'});

router.post("/register", function (req, res, next)
{
  var name = req.body.name;
  var type = req.body.type;
  var data = req.body.data;
  var domain_name = req.body.domain_name;

  if(!name)
  {
    return res.status(400).send("name is empty");
  }  

  if(!type)
  {
    return res.status(400).send("type is empty");
  }  

  if(!data)
  {
    return res.status(400).send("data is empty");
  }


    api.domainRecordNew(domain_name, {
        type : req.body.type, 
        name : req.body.name,
        data : req.body.data,
        }).then(function (droplets)
    {
        res.json(droplets);
    });

}) 

module.exports = router;