During the last few days, you might experience the issue while connecting to WordPress API. The error looks somehow like this:
WP HTTP API Error: cURL error 60: SSL certificate problem: certificate has expired.
This issue is caused by the expired Let’s Encrypt certificate (expired on September 30th). If an automatic update of WordPress is not an option for you, you should manually update the certificate. First, you should download the certificate file from the official WordPress repository:
Once downloaded, upload it to your WordPress installation to the ‘/wp-includes/certificates’ directory. You will see that such a file already exists – you should replace the old one with the new one.
PS: the same issue also occurs in Joomla
It looks like the same issue occurs in Joomla. If you want to adjust the certificate file manually, download this file:
and place it into the folder of ‘/libraries/src/Http/Transport’ – the file name is cacert.pem and, as it is with WordPress, you should replace the existing file with the newly downloaded version of the certificate.