curl --request POST \
  --url https://api.example.com/api/v2/external/billing/checkout \
  --header 'Content-Type: application/json' \
  --data '
{
  "credits_amount": 123,
  "success_url": "<string>",
  "cancel_url": "<string>"
}
'

{
  "checkout_url": "<string>",
  "session_id": "<string>"
}