Any to, bto, cc, bcc, and audience properties specified on the object MUST be copied over to the new Create activity by the server.

Requirement

Any to, bto, cc, bcc, and audience properties specified on the object MUST be copied over to the new Create activity by the server.

Origin

The origin of this requirement is a quote from the ActivityPub specfiication:
prefixThe Location value returned by the server should be the URL of the new Create activity (rather than the object).
Any to, bto, cc, bcc, and audience properties specified on the object MUST be copied over to the new Create activity by the server.
suffix Example 15: Object with audience targeting
https://www.w3.org/TR/activitypub/ , § 6.2.1

id

urn:uuid:f3725db1-1e6b-4d20-9cea-a49ef4291e9f

uuid

f3725db1-1e6b-4d20-9cea-a49ef4291e9f

Full JSON

{
  "id": "urn:uuid:f3725db1-1e6b-4d20-9cea-a49ef4291e9f",
  "uuid": "f3725db1-1e6b-4d20-9cea-a49ef4291e9f",
  "type": "Behavior",
  "content": "Any to, bto, cc, bcc, and audience properties specified on the object MUST be copied over to the new Create activity by the server.\n",
  "context": [
    "https://www.w3.org/TR/activitypub/",
    {
      "name": "6.2 Create Activity",
      "id": "https://www.w3.org/TR/activitypub/#create-activity-outbox"
    },
    {
      "name": "6.2.1 Object creation without a Create Activity",
      "id": "https://www.w3.org/TR/activitypub/#object-without-create"
    }
  ],
  "tag": [
    {
      "name": "ActivityPubServer",
      "id": "https://socialweb.coop/tag/ActivityPubServer"
    }
  ],
  "origin": {
    "source": "https://www.w3.org/TR/activitypub/",
    "section": {
      "id": "https://www.w3.org/TR/activitypub/#object-without-create",
      "name": "Object creation without a Create Activity",
      "branch": [
        6,
        2,
        1
      ]
    },
    "selector": {
      "type": "TextQuoteSelector",
      "prefix": "The Location value returned by the server should be the URL of the new Create activity (rather than the object). \n",
      "exact": "Any to, bto, cc, bcc, and audience properties specified on the object MUST be copied over to the new Create activity by the server.\n",
      "suffix": "Example 15: Object with audience targeting\n"
    }
  },
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    "https://socialweb.coop/ns/testing/context.json"
  ]
}

Links