public static List<UserPayer> getAllPayees(String myUid) {
        List<String> bids = new ArrayList<>();

        //asynchronously retrieve all documents
        ApiFuture<QuerySnapshot> future = db.collection("debts").get();
        // future.get() blocks on response
        List<QueryDocumentSnapshot> documents = null;
        try {
            documents = future.get().getDocuments();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

        for (QueryDocumentSnapshot document : documents) {
            System.out.println(document.getId() + "\n");
            bids.add(document.getId());
        }

        List<UserPayer> users = new ArrayList<>();
        for (String s: bids) {
            List<UserPayer> temp = getPayers(s);
            for (UserPayer: temp) {
                if (u.uid.equals(myUid)) {
                    users.add(u);
                }
            }
        }

        return users;
    }