Error saving field in mongoDB

I am creating a REST api with a Node and MongoDB I have a Group model in this way:

'use strict'

const mongoose = require('mongoose')
const Schema = mongoose.Schema

const GroupSchema = Schema({
  name: String,
  team1: String,
  team2: String,
  team3: String,
  team4: String
})
module.exports = mongoose.model('group', GroupSchema)

In my index.js file I have a post route to save info in the model:

app.post("/api/groups", (req, res)=>{
  console.log('POST /api/groups')
  console.log(req.body)

  let group = new Group()

  group.name = req.body.name
  group.team1 = req.body.team1
  group.team2 = req.body.team2
  group.team3 = req.body.team3
  group.team4 = req.body.team4

  group.save((err, groupStored) => {
    if (err) res.status(500).send({message: 'Error al guardar'})
    res.status(200).send({group: groupStored}) 
  })
})

I'm testing with Postman and keeping everything right except the Name field, no matter what name you put it simply does not save values other than team1, team2, team3 and team4.

When I do console.log (req.body) it shows the complete Json object:

  { 
  name: 'Grupo A',
  team1: 'Colombia',
  team2: 'Argentina',
  team3: 'Peru',
  team4: 'Brasil' 
  }

But then when checking in the BD it shows me:

{
"_id": {
    "$oid": "5ad50808763e0a0488e45b7b"
},
"team1": "Egipto",
"team2": "Rusia",
"team3": "Arabia Saudita",
"team4": "Uruguay",
"__v": 0
}