A Coupon cannot be used unless it has codes associated with it.
Each coupon code has a user specified identifier (code) that must be unique across all active coupon campaigns. It's usage may be limited or left open for unlimited use. Usage of coupons are tracked at the code level to measure the efficacy of your coupon campaign.
The list of codes for a given coupon would typically be specified during coupon creation within the codes property. Alternately, you may use these endpoints to operate at a per-code level.
{
"id": "5acc50ef07876cf24d8b456f",
"code": "23voucher",
"coupon": {
"id": "5acc50ef07876cf24d8b456c"
},
"status": 100,
"orders": [],
"uses": 0
}