In flutter How to save a list to firebase

got the answer going through the link provided by @Aldy Yuan

List<String> points1=[];
  List<String> toList1() {

    _points.forEach((item) {
      points1.add(item.toString());
    });

    return points1.toList();
  }

And then i add toList1 in firestore

onPressed: ()=>Firestore.instance.collection('points').add({"point":toList1()}),

Its because you can't save a list of Objects as a field of a document ( unless each list item as a document ) you can mostly add a list of primitive data types as a field of a doc (List<String>, List<int> ... ) , Offset is an object which is not a valid argument since it's not a primitive and that's why it is throwing your error.