Analytics Conversations Aggregates 400 on interval granularity

Running a custom interval report via the Analytics Conversations Aggregates API and hitting a 400 Bad Request. The payload looks valid based on the schema, but the service rejects the granularity setting. Here’s the JSON I’m sending:

{
 "query": {
 "groupBy": ["queue.id"],
 "aggregations": [{"type": "sum", "metric": "duration"}],
 "interval": {
 "start": "2023-10-01T00:00:00Z",
 "end": "2023-10-01T23:59:59Z",
 "granularity": "PT15M"
 }
 }
}

The error message is vague: “Invalid query parameter: interval.granularity”. I’ve tried PT1H and PT1D, both work fine. The issue seems specific to sub-hourly buckets. The docs mention a max of 10,000 intervals, which shouldn’t be an issue here since 15 minutes over 24 hours is only 96 buckets. Is there a hidden limit on granular intervals for conversation aggregates specifically, or is this a bug in the v2 endpoint? No SDK involved, just raw HTTP POST to /api/v2/analytics/conversations/aggregates.