"type": "customer_subscriptions",
"self": "https://yourdomain.commercelayer.io/api/customer_subscriptions/xYZkjABcde"
"created_at": "2018-01-01T12:00:00.000Z",
"updated_at": "2018-01-01T12:00:00.000Z",
"reference": "ANY-EXTERNAL-REFEFERNCE",
"reference_origin": "ANY-EXTERNAL-REFEFERNCE-ORIGIN",
"self": "https://yourdomain.commercelayer.io/api/customer_subscriptions/xYZkjABcde/relationships/customer",
"related": "https://yourdomain.commercelayer.io/api/customer_subscriptions/xYZkjABcde/customer"