Updating event attendees in Calendar list (type 106)

[EdAlexander]

using pnp in spfx webpart and can create/update/delete event items without issue as long as i don't try to add attendees.

getting error when:

await sp.web.lists.getByTitle('Calendar').items.add({
          Title: item.Title, 
          Description: item.Description,
          EventDate: item.StartTime,
          EndDate: item.EndTime,
           Attendees: item.Attendees,
        }).then().catch(addError => alert("An error has occurred:" + JSON.stringify(addError)));

results in alert:
An error has occurred:{"response":{},"status":400,"statusText":"","isHttpRequestError":true}

What do i need to pass to Attendees? userid? email? (i have tried many options including { emailAddress: 'xxx@sldkfjsd.com', name: 'full name',}

Any hints appreciated.