curl --request POST \
  --url https://api.example.com/agents/spans/custom-attrs/schema \
  --header 'Content-Type: application/json' \
  --data '
{
  "project_id": "<string>",
  "query": {
    "$expr": {
      "$and": [
        {
          "$literal": "<string>"
        }
      ]
    }
  },
  "started_after": "2023-11-07T05:31:56Z",
  "started_before": "2023-11-07T05:31:56Z",
  "limit": 200,
  "offset": 0
}
'

{
  "attributes": [
    {
      "key": "<string>",
      "span_count": 123
    }
  ],
  "limit": 200,
  "offset": 0,
  "has_more": false
}