curl --request GET \
  --url https://api.atlas.co/functions/v1/coupons/{coupon_id} \
  --header 'Authorization: Bearer <token>'

{
  "id": "<string>",
  "object": "coupon",
  "name": "<string>",
  "percent_off": 123,
  "amount_off": 123,
  "currency": "<string>",
  "duration": "<string>",
  "duration_in_months": 123,
  "max_redemptions": 123,
  "times_redeemed": 123,
  "redeem_by": 123,
  "applies_to": {
    "products": [
      "<string>"
    ]
  },
  "valid": true,
  "metadata": {},
  "created": 123
}