My OpenVPN connection does not go online. I get the error message "certificate not yet valid"

This usually means that your device's date set incorrectly. Your certificate is literally not valid yet, as your device is in the past. You can set the correct date and time under Administration → Time. See also How to ensure a regular update of the clock time? and What rules are required for an external firewall to access the icom Connectivity Suite - VPN?.