All issuance requests are subject to a Failed Validation limit of 5 failures per account, per hostname, per hour. You should receive the following error message from your ACME client when you’ve exceeded the Failed Validation limit:
too many failed authorizations recently: see https://letsencrypt.org/docs/failed-validation-limit/
The ‘authorizations’ that this error refers to are the result of authorization requests, sent by your ACME client, to validate control over a domain name before we can issue or renew a certificate. This error indicates that the multiple requests for validation were sent successfully but all attempts to validate have failed.
Subscribers who hit the Failed Validation limit often do so due to a misconfiguration in their environment.
HTTP-01 or TLS-APLN-01
For ACME clients requesting authorization via the HTTP-01 or TLS-APLN-01 validation methods, the problem usually stems from a network or firewall configuration which makes it impossible for our validation servers to reach the server that the request was sent from.
ACME clients requesting authorization via the DNS-01 validation method usually require that you create a CNAME record in your main DNS zone which allows the ACME client to set the required DNS records during the validation process. Failed DNS-01 validations are usually the result of missed steps or typos during this initial setup process.
When troubleshooting or testing the deployment of your applications we encourage you to configure your ACME client to use our staging environment. Rate limits for our staging environment are significantly higher.
If you’re not sure how to configure your ACME client to use our staging environment or you need some help debugging, we encourage you to request help on our community forum.
Requesting an Override
Overrides are not available for the Failed Validation limit.