curl -X POST 'https://api.goatpay.com.br/v1/coupons/validate' \
  -H 'X-API-Key: gp_live_SUA_CHAVE' \
  -H 'Content-Type: application/json' \
  -d '{
    "code": "VERAO10",
    "amount": 100,
    "paymentLinkId": "clx_link",
    "productId": "clx_product"
  }'

{
  "success": true,
  "message": "Cupom válido",
  "data": {
    "couponId": "clx_coupon",
    "code": "VERAO10",
    "discountType": "PERCENT",
    "discountValue": 10,
    "discountAmount": 10,
    "amountOriginal": 100,
    "amountFinal": 90
  },
  "requestId": "req_abc"
}