Validation fails when DNS TTL exceeds Railway renewal window?

When adding a custom domain to Railway, the platform automatically provisions a managed TLS certificate using Let's Encrypt. The goal is to guarantee that the certificate is issued and renewed successfully even when the domain's DNS TTL is set higher than Railway's 60‑day renewal interval. However, Railway's internal DNS resolver caches responses for up to five minutes, and if the TTL exceeds the renewal window the ACME validation challenge can fail silently because the cached record no longer matches the challenge token.

It is unclear whether Railway retries the ACME challenge after a DNS cache miss, what TTL threshold triggers the silent failure, and whether there is a mechanism to purge the internal resolver cache without waiting for the natural expiry. What is the maximum DNS TTL that Railway's ACME client tolerates before challenge validation fails? Does Railway retry ACME challenges after a DNS cache miss, or rely solely on the initial attempt? Is there a way to force Railway to refresh its internal DNS resolver cache for a domain without waiting five minutes?