src/Api/UrlGenerator.php
public function relatedResource($resourceType, $id, $relationshipKey, array $queryParams = [])
    {
        return $this->resource(RouteName::related($resourceType, $relationshipKey), $id, $queryParams);
    }
public function relatedResource($resourceType, $id, $relationshipKey, array $queryParams = [])
    {
        return $this->resource(RouteName::related($resourceType, $relationshipKey), $id, $queryParams);
    }
Get a link to a resource object's related resource.

@param $resourceType
@param $id
@param $relationshipKey
@param array $queryParams
@return string