curl --request POST \
  --url 'https://api.nsr.stateset.com/api/v1/billing/checkout' \
  --header 'X-API-Key: YOUR_API_KEY' \
  --header 'Content-Type: application/json' \
  --data '{
  "cancel_url": "string",
  "price_id": "string",
  "success_url": "string"
}'

{
  "checkout_url": "string"
}