Stripe checkout URL (new subscribers) or billing portal URL (existing subscribers). Redirect the user to this URL.
Human-readable message describing the action taken.
One of: already_subscribed, checkout_created, payment_issue.
{
"url": "https://checkout.stripe.com/c/pay/cs_live_...",
"message": "Complete checkout at the URL below to start your subscription.",
"status": "checkout_created"
}