Reading the error surface

Errors are data — and here they come in two shapes

See finding G6: the saved examples use both an RFC 7807-style envelope (title/detail/status/type) and a bare code/message envelope, with status sometimes a string and sometimes an integer. Your client should parse defensively:

def parse_error(payload: dict) -> tuple[int, str]:
    "Handle both envelopes observed in the saved examples."
    if "code" in payload:                      # {code, message}
        return int(payload["code"]), payload.get("message", "")
    return (                                   # {title, detail, status, type}
        int(payload.get("status", 0)),         # str OR int in the wild
        payload.get("detail") or payload.get("title", ""),
    )

The 4xx examples are a map of the server's rules

Each saved error example documents a real constraint:

• 403 on Step 3 — "The requested project is not in a state that allows this request." The lifecycle is enforced server-side; you cannot process a project twice, or before loading records.
• 400 on Create Profile — "The given data does not provide all necessary fields for generating an iWave profile." There is a minimum viable input; name and address fields must be parsed into their proper fields, not concatenated.
• 202 on Step 5 — not an error at all: "The requested project is still being processed." A 202 on a GET is unusual (it's typically a response to submission); here it means come back later — poll Step 4 and retry.
• 404 — same body for a missing profile and a missing project ("title": "An error occured" — typo in source), so distinguish by which URL you called, not by the body.

What you cannot learn from the examples

No 401, 429, or 5xx examples exist in the collection. The description tells you they happen ("Re-authenticate automatically if you receive a 401 Unauthorized error", "Implement exponential backoff for retries to avoid rate limit blocks") but shows no bodies for them. Build those handlers without assuming an envelope shape — you've already seen the server uses two.