Top up traffic balance

Purchase traffic balance using your account USD balance. Traffic is allocated per proxy type. Pricing is volume-based — the larger the `amount_gb`, the lower the per-GB rate (see `*_pricing_tiers` in `GET /reseller/balance`). The `cost` in the response reflects the tier applied to your purchased volume.

curl -X POST "https://api.soxway.io/reseller/topup-traffic" \  -H "Content-Type: application/json" \  -d '{    "amount_gb": 10,    "proxy_type": "residential"  }'

{
  "message": "string",
  "data": {
    "proxy_type": "string",
    "traffic_balance_gb": 0,
    "amount_added_gb": 0,
    "cost": 0
  }
}