POST /v3/instruments — bond-instrument

Create a fixed-income bond instrument.

Request:
{
  "data": {
    "type": "bond-instrument",
    "attributes": {
      "ccyCode":            "string (required) — ISO 4217 (e.g. USD, EUR, DKK)",
      "countryCode":        "string (required) — ISO 3166-1 alpha-2 issuer domicile (e.g. US, DE, DK)",
      "couponFrequency":    "string (required) — one of: quarterly, semiannually, annually",
      "datedDate":          "string, ISO 8601 (optional) — start date for accrued interest",
      "dayCountConvention": "string (required) — one of: actual/actual, 30/360, actual/360",
      "firstCouponDate":    "string, ISO 8601 (optional)",
      "maturityDate":       "string, ISO 8601 (optional)",
      "name":               "string (required) — display name",
      "securityIdentifier": "string (required) — external security identifier"
    }
  }
}

Response (201 Created):
{
  "data": {
    "id": "string",
    "type": "bond-instrument",
    "attributes": { /* same as request */ }
  }
}

Note: existing bonds may have `couponFrequency` or `dayCountConvention`
set to "other" — that value cannot be supplied when creating a new
bond, but it can appear on read.