If you followed my last article “How to host an https WordPress site on AWS EC2 with a Let’s Encrypt SSL certificate?” you know have a Let’s Encrypt generated SSL certificate for your WordPress.
Once in a while Let’s Encrypt will generate a new certificate if you scheduled the certbot-auto renew command.
You’ll then need to run the following commands to select the new certificate and avoid the “failed to start the Apache HTTP Server” error once your old certificate expired :