Problem type
Service temporarily unavailable
service-unavailable
What it means
On the management API: the payment provider cannot be reached (or billing is not set up on this deployment) when opening checkout or the billing portal, or the branding preview renderer is down. On an issuer host, /oauth/token and /oauth/device_authorization answer it when the rate limiter's store is unreachable. Not the request's fault.
What to do
Retry later; it is safe to. No Retry-After is sent.