curl -X POST https://api.kyren.top/v1/checkouts \
-H "Content-Type: application/json" \
-H "x-api-key: kyren_live_xxxxxxxxxxxx" \
-d '{
"productId": "prod_abc123",
"successUrl": "https://yoursite.com/success",
"cancelUrl": "https://yoursite.com/cancel",
"customerEmail": "customer@example.com",
"metadata": {
"userId": "user_456"
}
}'