Hi Polinet,
You are seeing that error because your web server has not been set up correctly to have an up-to-date root SSL certificates store, so it is not recognizing the certificate authority of the Codisto SSL certificate. Servers store root certificates and they should be kept up to date, so the server knows which certificates to trust based on who issued them.
The Codisto SSL certificate was nearing expiry and has been updated with an Amazon issued certificate but because your root SSL certificates store isn’t up to date you are seeing the error.
There are 2 options for fixing the problem:
1. Deleting the codisto.crt file which is in [‘basedir’].’/codisto.crt’
(If you are operating multi-site it is here: [‘basedir’].’/sites/’.get_current_blog_id().’/codisto.crt’ );
OR
2. Update the root certificate store on your server.
Please pass on to your web developers if you aren’t familiar with these instructions.