Start Build or Pro access via x402 USDC payment

Base64-encoded x402 v2 payment payload containing the EIP-3009 signed USDC transfer authorization. Omit on first request to receive payment details.

Selects the 2026-10 response contract. Send 2026-10-01; any dated version on or after it selects the same shapes. Without the header every response keeps its existing shape. With it:

• The data quality routes, /v1/status/coverage and /v1/symbols answer the standard {success, data, meta} envelope.
• Record times that are integer milliseconds by default become RFC 3339 UTC strings with millisecond precision, and the integer moves to a *_ms field: L4 resting-order timestamp (timestamp_ms), CVD buckets, HIP-3 oracle reads, Lighter and Lighter on Robinhood Chain liquidations and liquidation volume. Levels and trigger-levels snapshot_ts become RFC 3339 with snapshot_ts_ms.
• Error bodies carry the contract error_code names: invalid_parameter instead of invalid_query_params and invalid_path_params, historical_depth_exceeded instead of history_window_exceeded, and historical_range_exceeded instead of request_range_exceeded; a malformed cursor that fails to parse answers 400 invalid_cursor instead of invalid_query_params. With 0xArchive-Version: 2026-10-01, malformed cursors on trades, liquidations, L2 and L4 diffs, order history, TP/SL and order-flow routes answer 400 invalid_cursor. Without the header, the first six route families treat a malformed cursor as no cursor and return the first page; order flow answers 400 invalid_query_params. Malformed trade time inputs answer 400 invalid_time_range with the header and 400 invalid_query_params without it.

The response echoes the selected version in its own 0xArchive-Version header.