Securing your website with Let's Encrypt involves domain validation through the ACME protocol. However, issues like mismatched challenges can arise due to mishandled AAAA records.

In recent times, domain providers have begun including AAAA records, but some users may only update the A record. It's crucial to understand that during domain validation using the HTTP-01 challenge, Let's Encrypt favors AAAA records over A records. This preference can divert the validation request to a different server if AAAA records are not accurately configured. You will observe error like 403 :: urn:ietf:params:acme:error:unauthorized :: The key authorization file from the server did not match this challenge. Expected \"something\" (got \"somethingElse\") in your ACME client like certbot or in the proxy responsible for managing SSL certificates like Traefik.

To address this, update the AAAA records if your server has an IPv6 IP. Alternatively, if your server doesn't support IPv6, consider removing the AAAA records for the respective domain name.

This adjustment is essential for preventing validation errors and ensuring a smooth process when obtaining your Let's Encrypt certificate.