Retrieve a promotion code 

{
  "id": "promo_1MiM6KLkdIwHu7ixrIaX4wgn",
  "object": "promotion_code",
  "active": true,
  "code": "A1H1Q1MG",
  "promotion": {
    "type": "coupon",
    "coupon": "nVJYDOag"
  },
  "created": 1678040164,
  "customer": null,
  "expires_at": null,
  "livemode": false,
  "max_redemptions": null,
  "metadata": {},
  "restrictions": {
    "first_time_transaction": false,
    "minimum_amount": null,
    "minimum_amount_currency": null
  },
  "times_redeemed": 0
}