curl --request POST \
  --url https://sandbox-api.violet.io/v1/checkout/cart/{cart_id}/customer \
  --header 'Content-Type: application/json' \
  --header 'X-Violet-App-Id: <x-violet-app-id>' \
  --header 'X-Violet-App-Secret: <x-violet-app-secret>' \
  --header 'X-Violet-Token: <x-violet-token>' \
  --data '{
  "customer": {
    "first_name": "Super",
    "last_name": "Mario",
    "email": "super@mar.io"
  }
}'

{
  "id": 10000,
  "token": "fz8x7gksdjsy2p9fdlonw7k9svwjso4b",
  "user_id": 10000,
  "app_id": 10000,
  "developer_id": 10000,
  "customer": {
    "user_id": 10000,
    "first_name": "Super",
    "last_name": "Mario",
    "email": "super@mar.io",
    "name": "Super Mario"
  },
  "bags": [],
  "shipping_address": null,
  "billing_address": null,
  "payment_method": null,
  "sub_total": 0,
  "shipping_total": 0,
  "tax_total": 0,
  "discount_total": 0,
  "total": 0,
  "app_order_id": "00100100",
  "status": "IN_PROGRESS",
  "is_guest": true,
  "date_created": "2017-06-15T01:01:01+0000",
  "date_last_modified": "2017-06-15T01:01:01+0000",
  "priced": false,
  "wallet_based_checkout": false,
  "currency": "USD",
  "channel": "APP",
  "currency_symbol": "$",
  "stripe_key": "pk_test_UHg8oLvg4rrDCbvtqfwTE8qd",
  "payment_intent_client_secret": "pi_vw8krrsvposl347c5l7x1nt5_secret_vbcw5t2bze37iptq430tmx7s",
  "payment_transactions": null,
  "intent_based_checkout": true,
  "guest": true,
  "order_id": 11111
}