MYSQL getting SUM through joins

I'm looking for a possible solution that will give me TOP 3 users from users table who are ordered based on the turnover they made.

So here is my table schema for users and transactions table.

users TABLE

id     inviter_id
1      1
2      1
3      1
4      1
5      2
6      3
7      5
8      6
9      1
10     3
11     9
12     1
13     5
14     7
15     11

EXPLANATION : The id represents user's unique ID and inviter_id represents the ID that invited the user.

transactions TABLE

id            payer _id      amount
1             2              200
2             2              100
3             2              50
4             2              10
5             3              400
6             4              200
7             5              100
8             6              50
9             7              100
10            8              50
11            9              50
12            10             100 
13            11             400
14            2              200
15            2              100
16            2              50
17            2              10
18            4              500

Here payer_id represents the users in users table.

Desired Output :

user_id       turnover
//ID 1 should not be included in this table.
2             100         //ID 5 in `users` is referral of ID 2 so summing whatever ID 5 from `transactions` table using `payer_id` column we get : 100 (Sme process for other rows too)
3             150         //ID3's referrals : 6,10 | 50+100
4             0           //ID4's invited no one
5             100         //ID5's referrals : 7,13 | 100
6             50          //ID 6's referrals : 8 | 50
7             100         // ID 7's referrals : 14 | 0 (No rows for ID 14 in transactions table)
8             0           //No referrals invited
9             400         //ID9's referrals : 11 | 400
10            0           //No referrals invited
11            0           //ID11's referrals : 14 | 0 (No rows in txn table)
12            0           //No referrals invited
13            0           //No referrals invited
14            0           //No referrals invited
15            0           //No referrals invited

FIRST let me explain how I calculate turnover :

For each id from users table, Let's take id:1 as example. I check the 'inviter_id' column for 2. So whoever has the value as 2 in inviter_id column, those ids are considered as id 2's referral. So I need the sum of amount all the referrals of id 2 has paid. Similarly for other ids and they should be sorted by the highest turnover.

What I tried so far : here is my code.

        select u.id AS user_id, u.address AS address, SUM(turnover) AS turnover
        from users u left join
             (select ur.id, ur.inviter_id, SUM(mt.userTurnover) as turnover
                    from users ur left join

                            (select m.payer_id, SUM(m.amount) as userTurnover
                            from matrix m where m.created >= $content_start AND m.type = 'escrow'
                            group by m.payer_id
                            ) mt
                            on mt.payer_id = ur.id

                    where ur.created >= $content_start
              group by ur.inviter_id
             ) ui
             on ui.inviter_id = u.id
                 WHERE u.id != 1 AND u.id != 2 AND u.id != 3 AND u.id != 4
        group by u.id
        order by turnover desc  LIMIT 10;

I'm getting the sum of amounts of the user itself instead of the user's each and every referral's paid amount.