curl --request GET \
  --url https://api.hubapi.com/email/public/v1/subscriptions

{
  "subscriptionDefinitions": [
    {
      "active": true,
      "portalId": 12345,
      "description": "The default unsubscribe list that all emails in your hub will use",
      "id": 7,
      "name": "Default"
    },
    {
      "active": true,
      "portalId": 12345,
      "description": "Our weekly newsletter informing you about our new happenings",
      "id": 146,
      "name": "Weekly Newsletter"
    }
  ]
}