Build one unsigned transaction from an IDL instruction

[
  {
    "scheme": "exact",
    "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
    "payTo": "WzMaL78srutrF6CsxEkWuhMaDF5HZA6jNRaEPengqpb",
    "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "amount": "2000",
    "maxTimeoutSeconds": 60
  }
]

{
  "bazaar": {
    "info": {
      "input": {
        "body": {
          "accounts": {
            "mint": "<base58 pubkey>"
          },
          "args": {
            "amount": "1000000",
            "max_sol_cost": "100000"
          },
          "instruction": "buy",
          "payer": "<base58 pubkey that will sign>",
          "programId": "6EF8rrecthR5Dkzon8Nwu78hRvfCKubJ14M5uBEwF6P"
        },
        "bodyType": "json",
        "method": "POST",
        "type": "http"
      },
      "output": {
        "example": {
          "resolvedAccounts": [],
          "signers": [
            "<pubkey>"
          ],
          "transaction": "<base64 v0 tx>"
        },
        "type": "json"
      }
    },
    "schema": {
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "properties": {
        "input": {
          "additionalProperties": false,
          "properties": {
            "body": {
              "properties": {}
            },
            "bodyType": {
              "enum": [
                "json",
                "form-data",
                "text"
              ],
              "type": "string"
            },
            "method": {
              "enum": [
                "POST",
                "PUT",
                "PATCH"
              ],
              "type": "string"
            },
            "type": {
              "const": "http",
              "type": "string"
            }
          },
          "required": [
            "type",
            "method",
            "bodyType",
            "body"
          ],
          "type": "object"
        },
        "output": {
          "properties": {
            "example": {
              "type": "object"
            },
            "type": {
              "type": "string"
            }
          },
          "required": [
            "type"
          ],
          "type": "object"
        }
      },
      "required": [
        "input"
      ],
      "type": "object"
    }
  }
}

curl "https://the-composer.fly.dev/tx/build"
# -> 402 Payment Required, accepts[] lists how to pay
# retry with a PAYMENT-SIGNATURE (or PAYMENT header) once paid

const res = await fetch("https://the-composer.fly.dev/tx/build");
if (res.status === 402) {
  const { accepts } = await res.json();
  // pay one of accepts[] via an x402 client, then retry with the payment header
}

import httpx
res = httpx.get("https://the-composer.fly.dev/tx/build")
if res.status_code == 402:
    accepts = res.json()["accepts"]
    # pay one of accepts[] via an x402 client, then retry with the payment header