Analytics API aggregation query grouping by queue and media type returning empty

I’m trying to pull aggregated interaction data from the Genesys Cloud Analytics API. The goal is to group results by both queue and mediaType to see call vs chat volumes per queue. I’m sending a POST to /api/v2/analytics/interactions/queues/query with the following JSON payload:

{
 "groupBy": ["queue", "mediaType"],
 "dateFrom": "2023-10-01T00:00:00.000Z",
 "dateTo": "2023-10-02T00:00:00.000Z",
 "select": ["queueName", "mediaType", "totalInteractions"]
}

The request returns a 200 OK, but the entities array is empty. I’ve verified that there was definitely traffic in these queues during that window. If I remove mediaType from the groupBy array, I get valid data for the queues. It seems like adding a second dimension breaks the query. Is there a specific syntax requirement for multi-dimensional grouping in this endpoint? I’ve checked the documentation but it’s pretty sparse on examples for combined groupings.