curl -X GET 'https://api.goatpay.com.br/v1/subaccount/balance?externalReference=loja-parceiro-a' \
  -H 'X-API-Key: gp_live_SUA_CHAVE'

{
  "success": true,
  "message": "Saldo da subconta",
  "data": {
    "id": "clx_subconta",
    "balance": {
      "availablePadrao": 1500,
      "pendingPadrao": 0,
      "lockedPadrao": 0,
      "spendablePadrao": 1500
    }
  },
  "requestId": "req_abc123"
}