POST /api/v2/recordings/recordings/start returns 400 for specific conversation IDs

We are instrumenting recording start/stop events in New Relic. The goal is to capture custom attributes when a recording begins. The POST request to /api/v2/recordings/recordings/start fails with a 400 Bad Request for some conversation IDs, even though the conversationId is valid and the user has the required permissions. The payload is:

{
 "conversationId": "123e4567-e89b-12d3-a456-426614174000",
 "recordingType": "conversation"
}

The error message says Conversation not found. This works fine for other calls. Is there a delay before the recording API recognizes the conversation?