curl --request GET \
  --url https://api-next.ofauth.com/v2/access/statistics/mass-messages/chart \
  --header 'apiKey: <api-key>'

{
  "purchases": {
    "chart": [
      {
        "date": "<string>",
        "count": 123
      }
    ],
    "total": 123,
    "delta": 123,
    "gross": 123
  },
  "messages": {
    "chart": [
      {
        "date": "<string>",
        "count": 123
      }
    ],
    "total": 123,
    "delta": 123,
    "gross": 123
  }
}