curl --request POST \
  --url https://api.virtuoussoftware.com/api/Event/{eventId}/Attendees \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "contactIndividualId": "<integer>",
  "customFields": [
    {
      "name": "<string>",
      "value": "<string>",
      "displayName": "<string>"
    },
    {
      "name": "<string>",
      "value": "<string>",
      "displayName": "<string>"
    }
  ]
}
'

{
  "id": "<integer>",
  "eventInvitationUrl": "<string>",
  "contactId": "<integer>",
  "contactIndividualId": "<integer>",
  "invitee": "<string>",
  "contactUrl": "<string>",
  "event": "<string>",
  "eventId": "<integer>",
  "eventViewUrl": "<string>",
  "location": "<string>",
  "startDateTime": "<string>",
  "endDateTime": "<string>",
  "timeZone": "<string>",
  "rsvp": "<string>",
  "attended": "<string>",
  "emailAddress": "<string>",
  "invited": "<string>",
  "emailStatus": "<string>",
  "emailSent": "<string>",
  "createDateTimeUtc": "<dateTime>",
  "createdByUser": "<string>",
  "modifiedDateTimeUtc": "<dateTime>",
  "modifiedByUser": "<string>",
  "customFields": [
    {
      "name": "<string>",
      "value": "<string>",
      "displayName": "<string>"
    },
    {
      "name": "<string>",
      "value": "<string>",
      "displayName": "<string>"
    }
  ]
}