acme cron error renew

Since a few days I get a daily error e-mail for only 2 of my domains, not for all of them:

Subject: Cron <root@cwp> "/root/.acme.sh"/acme.sh --cron --home "/root/.acme.sh/cwp_certs" > /dev/null

Please specify at least one validation method: '--webroot', '--standalone', '--apache', '--nginx' or '--dns' etc.
[Thu Mar 23 00:02:13 CET 2023] Error renew domain.com

The weird thing is that the certificate for these domains is actually valid and https works normally as always. And I haven't actively changed anything.

Any idea what's going on, and how to get rid of this error message?

Confirm there is a validation method (usually webroot) in your conf files for those domains:
/root/.acme.sh/cwp_certs/www.domain.com/www.domain.com.conf
/root/.acme.sh/cwp_certs/www.domain.com/www.domain.com.csr.conf
You didn't manually edit these files, did you? You could delete the offending domains in CWP under Web Server > SSL Certificates and then re-add them.