curl --request GET \
  --url https://api.hubapi.com/crm/objects/2025-09/{objectType}/{objectId}/associations/{toObjectType} \
  --header 'Authorization: Bearer <token>'

{
  "results": [
    {
      "associationTypes": [
        {
          "category": "HUBSPOT_DEFINED",
          "typeId": 123,
          "label": "<string>"
        }
      ],
      "toObjectId": "<string>"
    }
  ],
  "paging": {}
}