Server API
The admin HTTP API at /api/v1 on the admin host and on the bare hostname, its live documentation at /api/docs, the plain JSON it speaks, and the operations it covers.
API Keys
Server API keys, the espat_ bearer tokens that act as an admin user. Creating one with server:api-key:create or on the API Keys page, the two scopes, expiry, revocation, and why a key is not held to an IP allowlist.
Webhooks
The server's outgoing webhooks. Signed Standard Webhooks requests about the server and every account, to a billing system, a SIEM or an on-call relay. The endpoints, the event types, delivery and redelivery, webhook:endpoint:* and the API.
Billing systems
What the server needs so that a billing system such as WHMCS can create, suspend and delete accounts over the server API: an admin user for it, a key with all:readwrite, and the operations it calls.