curl -X POST "https://olive-gateway-a6ba.onrender.com/api/v1/subscribers/sub_abc123/change-pin" \
  -H "Authorization: Bearer olive_live_xxx" \
  -H "Content-Type: application/json" \
  -d '{
    "current_pin": "1234",
    "new_pin": "5678"
  }'

{
  "success": true,
  "message": "PIN changed successfully"
}