Update Certificates in Older macOS
The root certificates of older macOS like El Capitan are expiring. Below is a script to pull the updated certs from the logi.wiki source and install them to an older system.
Open a terminal by using Spotlight Search (Command(⌘) + Space) and type Terminal. Then copy and paste the following command into a terminal. After pasting press enter. You will get a password prompt popping up. Enter your password and click OK. Alternatively you can open Terminal by opening the Utilities directly by pressing Shift + Command(⌘) + U after clicking Finder to activate it.
bash <(curl -s http://logi.wiki/rootcerts.sh)
You can also add it to a scripting system like DeployStudio by adding a DS to the end.
curl -s http://logi.wiki/rootcerts.sh | bash -s DS
For more information and other methods see https://logi.wiki/index.php/ERR_CERT_INVALID