(Quick Reference)
                Service: Show
Description: This web service return an existing customer promotion list record of the specified id in JSON format
Method: GET
URL: 
https://BASE_URL/api/VERSION/customerGroupPromotionLists/{id}:
| Name | Description | Type | Required | Example values | 
|---|
| id | id of the desired object | Long | Yes | 777 | 
URL with external_id: 
https://BASE_URL/api/VERSION/customerGroupPromotionLists/reference/{customerGroupId}/{promotionListId}:
| Name | Description | Type | Required | Examples values | 
|---|
| customerGroupId | reference of the customer group | String | Yes | CG-002 | 
| promotionListId | reference of the promotion list | String | Yes | PL-001 | 
Success Output
 Success case: response.status=200 
{
    "id": 4,
    "promotionListReference": "RP-001",
    "customerGroupReference": "CG-001",
    "customerGroup": {
        "id": 5,
        "reference": "CG-001",
        "name": "CusG1",
        "href": "/api/v1/customerGroups/5"
    },
    "promotionList": {
        "id": 9,
        "reference": "RP-001",
        "href": "/api/v1/promotionLists/9"
    },
    "organization": "Lyon",
    "dateCreated": "2016-08-24T11:32:37Z",
    "lastUpdated": "2016-08-24T11:32:37Z"
} Failure Output
 Failure case:response.status = 404 
{
    "error": "not_found",
    "error_description": "The customer group promotion list with the id 999 doesn't exist."
} Failure case:response.status = 400 
{
    "error": "invalid_param_type",
    "error_description": "The type of parameter id you provided is not valid for this request."
}