Watch up to 25 wallets and register one webhook (API key; a free key works, 3 wallets)

Body: { addresses: string[≤25], webhookUrl (https, port 443, public hostname), scoreDropPoints? (1–550; omit = no score_drop events — there is NO default threshold), subscriptionId? (add to an existing subscription), acknowledgement: { accepted: true, version } } — the consumer-use acknowledgement (no use for consumer credit/insurance/employment/housing decisions under FCRA/ECOA) is REQUIRED and stored with a timestamp. A test ping is sent first; if it is not answered 2xx nothing is created. The signing secret (X-XRPLHub-Signature: v1=HMAC-SHA256 over '<timestamp>.<body>') is returned ONCE. Events: score_drop, sanctions_hit, sanctions_delisted, first_loan_observed, loan_overdue, loan_impaired, loan_defaulted (the loan events are dormant until XLS-66 activates, then fire automatically) and monitoring_degraded. Attested observations are sparse (baseline / change / event / weekly heartbeat) under the frozen monitor-observation-v1 canon; a score is included only when freshly computed.