MulterError: Unexpected field in node js

i'm trying to save the mulptile fields of files in mongodb with the use of multer,As im using form-data for selecting files. As per name fields file {name:'thumbnail'},{name:'trailer'},{name:'lessons'}] so i'm passing same in the postman but it showing an error: MulterError: Unexpected field

Where i'm passing wrong ,please help me thanks in advance

schema:-

  mongoose.Schema(
    {
      category:{ type: String },
      courseBy:{ type: String },
      thumbnail: { type: String, data:Buffer},
      about: { type: String },
      price : { type: String },
      is_free : { type:Boolean, default: false },
      tags : { type: String },
      comments : { type: String },
      ratings : { type: String },
      hours: { type : String },
      trailerVideo : {
        title:{ type:String },
        video: {
          type:String,data:Buffer
      }},
      ratingCount : { type: Number},
      lessons : [{ 
        _id: false,
        title : { type:String },
        video  : { type:String,data:Buffer }, 
      }]
    }
  )

creating an instane:-

 const trailer = {
    title: req.body.title,
    video: req.files.trailer[0].path,
  }

  const lessons = [{
    title: req.body.title,
    video: req.files.lessons[0].path
  }]

  const { category, courseBy, about, price, hours }  = req.body

  const courseFields = new Courses({  
    category: category,
    courseBy: courseBy, 
    thumbnail: req.files.thumbnail[0].path,
    about: about,
    price: price,
    hours: hours,
    ratingCount : 0,
    ratings : 0.0,
    trailerVideo: trailer,
    lessons: lessons
});

multer file

 const multer = require("multer"),    
   storage = multer.diskStorage({

destination: function(req, file, cb) {
  cb(null, 'uploads')
},

filename: function (req, file, cb) {
  cb(null, file.originalname);
}
});

const uploadImg = multer({storage: storage}).fields([{name:'thumbnail'},{name:'trailer'},{name:'lessons'}]);