got both and can tell that Mac Os is much more better for that...

meetups: [{ type: Schema.Types.ObjectId, ref: 'Meetup', }], better try with: meetups: { type: Schema.ObjectId, ref: 'Meetup' } and declare : const Schema = mongoose.Schema; (it will be the Schema inside the type: -Schema -) before: const GroupSchema = new Schema { Try to separate the model of the functions to establish a structure finishing the module file with: module.exports = mongoose.model('Group', groupSchema); and then the meetup function in another file. Hope it helps :)