为什么我不能从我的其余api将数据上传到mongodb

so am building a rest API to in node using express and mongoDB everything was running fine and am using postman to test my API the problem is I couldn't upload my data to the mongo db when i use const upost = await post.save() so the problem occurs in this line the reason for my conclusion is if i res.json(post) i can get the response i attached my response in the image below so my problem is i couldnt save my data to the db .....

编码:

const express = require('express')
const router = express.Router()
const csmodel = require('../models/pmodel')

router.get('/' , (req,res) => {
    res.send("inside db router")
});

router.post('/', async (req,res) => {
    const npost = new csmodel({
        sub2: req.body.sub2,
        sub1 : req.body.sub1})
    //res.json(npost)  //i could get response if i use this line
    try{
    const upost = await post.save() //but the problem occurs here 
    res.json(upost)//as the problem occurs on above line this line is not being executed
    }catch(err){
        res.json({
            message: err//am not receiving any error 
        })
    }
})


module.exports = router;

response from postman when i use .save() response from postman when i dont use .save()

所以我怎样才能将数据添加到我的数据库?