i have this model with username and email set uniqe to false

const UserSchema = new mongoose.Schema({
  username: {
    type: String,
    required: true,
    minlength: 3,
    maxlength: 20,
    unique: false,
  },
  email: {
    type: String,
    required: true,
    minlength: 5,
    maxlength: 64,
    lowercase: true,
    unique: false,
  },
  mailboxLink: {
    type: String,
    required: true,
    unique: true,
    default: nanoid(),
  },
  createdat: { type: String, default: dateJakarta },
});

and 1 user in my mongodb database

{"_id":{"$oid":"622eec9de7f66d1d633061e7"},"username":"jhon","email":"email@gmail.com","mailboxLink":"mfdYTDK","createdat":"2022-03-14 14:19:01","__v":0}

but when i'm trying to register the same username and email

userRouter.post("/register", async (request, response) => {
  const newUser = new userSchema(request.body); // body: {username, email}
  await newUser.save((err, user) => {
    if (err) {
      console.log(err);
    } else {
      const token = newUser.generateAuthToken();
      response.status(201).json({
        token,
        user,
        message: "Register successfully",
      });
    }
  });
});

i got this error from console.log(err);

MongoServerError: E11000 duplicate key error collection: PigeonProjekt.users index: email_1 dup key: { email: "email@gmail.com" }


  index: 0,
  code: 11000,
  keyPattern: { email: 1 },
  keyValue: { email: 'email@gmail.com' }

could someone help me solve this problem.