curl --request GET \
  --url https://app.nex.ai/api/developers/v1/relationships \
  --header 'Authorization: <api-key>'

{
  "data": [
    {
      "id": "789",
      "type": "one_to_many",
      "entity_definition_1_id": "123",
      "entity_definition_2_id": "456",
      "entity_1_to_2_predicate": "has",
      "entity_2_to_1_predicate": "belongs to",
      "created_at": "2024-01-15T10:00:00Z"
    }
  ]
}