POST /api/v2/conversations/{id} wrap-up code 400 error

Trying to set a wrap-up code via the API right after a call ends. The endpoint docs say to POST to /api/v2/conversations/calls/{conversationId}/participants/{participantId}/communications/{communicationId}/wrapup, but I’m getting a 400 Bad Request on the wrapupCode field.

Here’s the payload. What am I missing?

{
 "wrapupCode": {
 "id": "12345"
 }
}