beel-es Webhooks API
Outbound webhook subscriptions for real-time event notifications. Register HTTPS endpoints to receive event payloads when key actions occur (e.g. VeriFactu submission accepted/rejected by AEAT). All deliveries are signed with HMAC-SHA256 (`BeeL-Signature` header). Failed deliveries are retried on a fixed schedule: 7 attempts over about 3 days (3 attempts over about 11 minutes in sandbox); a `4xx` other than `408` and `429` is not retried.