<?php
namespace Api\V8\JsonApi\Helper;

use Api\V8\Helper\VarDefHelper;
use Api\V8\JsonApi\Response\LinksResponse;
use Api\V8\JsonApi\Response\RelationshipResponse;

class RelationshipObjectHelper
{
    /**
     * @var VarDefHelper
     */
    private $varDefHelper;

    /**
     * @param VarDefHelper $varDefHelper
     */
    public function __construct(VarDefHelper $varDefHelper)
    {
        $this->varDefHelper = $varDefHelper;
    }

    /**
     * @param \SugarBean $bean
     * @param string $uriPath
     *
     * @return RelationshipResponse
     */
    public function getRelationships(\SugarBean $bean, $uriPath)
    {
        $relationships = $this->varDefHelper->getAllRelationships($bean);
        asort($relationships);

        $relationshipsLinks = [];
        foreach (array_unique($relationships) as $module) {
            $linkResponse = new LinksResponse();
            $linkResponse->setRelated(
                sprintf('/%s/%s/%s', $uriPath, 'relationships', strtolower($module))
            );

            $relationshipsLinks[$module] = ['links' => $linkResponse];
        }

        return new RelationshipResponse($relationshipsLinks);
    }
}

<?php
namespace Api\V8\JsonApi\Helper;

use Api\V8\Helper\VarDefHelper;
use Api\V8\JsonApi\Response\LinksResponse;
use Api\V8\JsonApi\Response\RelationshipResponse;

class RelationshipObjectHelper
{
    /**
     * @var VarDefHelper
     */
    private $varDefHelper;

    /**
     * @param VarDefHelper $varDefHelper
     */
    public function __construct(VarDefHelper $varDefHelper)
    {
        $this->varDefHelper = $varDefHelper;
    }

    /**
     * @param \SugarBean $bean
     * @param string $uriPath
     *
     * @return RelationshipResponse
     */
    public function getRelationships(\SugarBean $bean, $uriPath)
    {
        $relationships = $this->varDefHelper->getAllRelationships($bean);
        asort($relationships);

        $relationshipsLinks = [];
        foreach (array_unique($relationships) as $relationshipName => $module) {
            $linkResponse = new LinksResponse();
            $linkResponse->setRelated(
                sprintf('/%s/%s/%s', $uriPath, 'relationships', $relationshipName)
            );

            $relationshipsLinks[$module] = ['links' => $linkResponse];
        }

        return new RelationshipResponse($relationshipsLinks);
    }
}

Replace the lower case module names in the relationship links in API responses by the actual relationship identifiers
Replace the lower case module names in the relationship links in API responses by the actual relationship identifiers
