getAliasProperties are not working for included relationships

[rduque1]

When I get a resource, the aliases for the properties are well done, but the aliases for the included relationships are not used.

{
    "data": [
        {
            "type": "coupon-referrals",
            "id": "11",
            "attributes": {
                "coupon-id": 34,
                "created-at": "2017-09-12 12:44:17",
                "id": 11,
                "order-id": 5830,
                "updated-at": "2017-09-12 12:44:17",
                "user-id": 2000000010
            },
            "relationships": {
                "order": {
                    "data": {
                        "type": "order",
                        "id": "5830"
                    }
                },
                "coupon": {
                    "data": {
                        "type": "coupon",
                        "id": "34"
                    }
                }
            }
        }
    ],
    "included": [
        {
            "type": "order",
            "id": "5830",
            "attributes": {
                "user_id": 2000000010,
                "payment_id": 5675,
                "apps": "[]",
                "products": "[{\"id\":2,\"quantity\":1,\"price\":1500}]",
                "shipped": 0,
                "shipping_costs": 0,
                "created_at": "2017-09-12 12:44:15",
                "updated_at": "2017-09-12 12:44:17"
            }
        },
        {
            "type": "coupon",
            "id": "34",
            "attributes": {
                "name": "REF2642b",
                "amount": 1000,
                "coupon_type": "referral-amount",
                "counter": 2,
                "max_counter": 2,
                "valid_from": "2017-09-12",
                "valid_to": "2018-09-12",
                "is_products_only": 1,
                "created_at": "2017-09-12 12:44:17",
                "updated_at": "2017-09-12 12:47:25"
            }
        }
    ],
    "links": {
        "self": {
            "href": "http://192.168.99.100:4200/api/coupon-referrals/11?page[number]=1&page[size]=10"
        },
        "first": {
            "href": "http://192.168.99.100:4200/api/coupon-referrals/11?page[number]=1&page[size]=10"
        },
        "last": {
            "href": "http://192.168.99.100:4200/api/coupon-referrals/11?page[number]=1&page[size]=10"
        }
    },
    "meta": {
        "page": {
            "total": 1,
            "last": 1,
            "number": 1,
            "size": 10
        }
    },
    "jsonapi": {
        "version": "1.0"
    }
}

As you can see the order has in the properties _ as in the mapping is defined in the aliases to use -.

<?php

namespace App\Api\V1\Mappings;

use App\Coupon;
use NilPortugues\Api\Mappings\JsonApiMapping;

class CouponMapping implements JsonApiMapping
{
    public function getClass()
    {
        return Coupon::class;
    }

    /**
     * Returns an array of properties that will be renamed.
     * Key is current property from the class. Value is the property's alias name.
     *
     * @return array
     */
    public function getAliasedProperties()
    {
        return [
            'coupon_type'       => 'coupon-type',
            'max_counter'       => 'max-counter',
            'valid_from'        => 'valid-from',
            'valid_to'          => 'valid-to',
            'is_products_only'  => 'is-products-only',
            'created_at'        => 'created-at',
            'updated_at'        => 'updated-at'
        ];
    }

    public function getIdProperties()
    {
        return ['id'];
    }
    /**
     * Returns an array containing the relationship mappings as an array.
     * Key for each relationship defined must match a property of the mapped class.
     *
     * @return array
     */
    public function getRelationships()
    {
        return [];
    }

    /**
     * Implement the remaining methods from NilPortugues\Api\Mappings\ApiMapping::getRequiredProperti
     */
     public function getRequiredProperties()
    {
        return [];
    }
}

It the same for the order relationship. What did I do wrong?