curl --request POST \
  --url https://api.salesbricks.com/api/v2/subscriptions/{subscription_id}/upgrade/{order_id}/sign \
  --header 'Content-Type: application/json' \
  --header 'X-SALESBRICKS-KEY: <api-key>' \
  --data '
{
  "redirect_url": "<string>"
}
'

{
  "url": "<string>"
}