Client used ACME TLS-SNI-01 domain validation to issue a certificate

I received the following email from Let’s Encrypt.
I’m new to NextCloud, how can I resolve this?

Action may be required to prevent your Let’s Encrypt certificate renewals from breaking.

If you already received a similar e-mail, this one contains updated information.

Your Let’s Encrypt client used ACME TLS-SNI-01 domain validation to issue a certificate in the past 60 days. Below is a list of names and IP addresses validated (max of one per account):


TLS-SNI-01 validation is reaching end-of-life. It will stop working temporarily on February 13th, 2019, and permanently on March 13th, 2019.
Any certificates issued before then will continue to work for 90 days after their issuance date.

You need to update your ACME client to use an alternative validation method (HTTP-01, DNS-01 or TLS-ALPN-01) before this date or your certificate renewals will break and existing certificates will start to expire.

Your message is a server/letsencrypt-problem and depends on the system you use.
For debian:

solved my issue.
For other OS you’ll find help here:

Thanks! I was on a lower version and updated thanks to you!