POST /v1/quotes
Idempotency-Key: 7f3c9e1a-…

{
  "source": { "asset": "USDT", "network": "tron" },
  "target": { "currency": "BRL", "amount": "189.90" },
  "expires_in": 15
}

→ 201 Created
{ "id": "qt_01J…", "rate": "5.4200",
  "source_amount": "35.32", "status": "quote.created" }