Retrieve a single call by its numeric id.

When to use. Drill-down to the full detail of one call, for example from a list row. Returns 404 if the id does not exist or is not visible to your API user.

Shape. { "calls": [ <call> ] }, a single-element array that matches the list endpoint's envelope.

Gateway note: custom call fields defined on the account can be used as filter keys (path segments, see the _filtered variant) and are returned on each record alongside the standard fields.