curl --request GET \
  --url https://macrobymark.com/api/forecast/series \
  --header 'X-API-Key: <api-key>'

{
  "series": [
    {
      "slug": "<string>",
      "provider": "<string>",
      "providerSeries": "<string>",
      "conceptKey": "<string>",
      "frequency": "<string>"
    }
  ]
}