code: protected function validateRelationships(): bool
      {
          if (!$this->dataHas('relationships')) {
              return true;
          }
  
          $relationships = $this->dataGet('relationships');
  
          if (!is_object($relationships)) {
              $this->memberNotObject('/data', 'relationships');
              return false;
          }
  
          $disallowed = collect(['type', 'id'])->filter(function ($field) use ($relationships) {
              return property_exists($relationships, $field);
          });
  
          $valid = $disallowed->isEmpty();
          $this->memberFieldsNotAllowed('/data', 'relationships', $disallowed);
  
          foreach ($relationships as $field => $relation) {
              if (!$this->validateRelationship($relation, $field)) {
                  $valid = false;
              }
          }
  
          return $valid;
      }
docs: Validate the resource relationships.
  
  @return bool