curl --request GET \
  --url https://api.hubapi.com/crm/v4/objects/{objectType}/{objectId}/associations/{toObjectType} \
  --header 'Authorization: Bearer <token>'

{
  "paging": {
    "next": {
      "after": "<string>",
      "link": "<string>"
    },
    "prev": {
      "before": "<string>",
      "link": "<string>"
    }
  },
  "results": [
    {
      "associationTypes": [
        {
          "category": "HUBSPOT_DEFINED",
          "label": "<string>",
          "typeId": 123
        }
      ],
      "toObjectId": "<string>"
    }
  ]
}