curl --request POST \
  --url https://api.thundercompute.com:8443/v1/checkout-usage \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '{}'

{
  "already_subscribed": true,
  "checkout_url": "<string>",
  "refresh": true,
  "retry_after_ms": 123
}