Procedure:
1. Activate Charles recording
2. Enter Ninja Saga
3. Go back to charles.
4. On the structure tab, right click "app.ninjasaga.com"
5. Choose breakpoints
6. Click Newbie Items Redeem Icon
7. Input whatever 10 digit code you want
8. Click "Claim Reward" button.
9. Wait until Charles breakpoints appear
10. Click "Edit Request" tab and click "amf"
11 Look for "[2] string"
12. Change "String" into "Boolean"
13. Change "false" into "true"
14. Click Red button to disable breakpoints.
15. Click "Execute".

SCREENSHOT