To use WSS (WebSocket Secure) charger must have synchronized time. Station normally uses NTP server to synchronize clock, but if station is under private APN you need to synchronize clock manually with computer connected to station. Second option is using private NTP server that is visible from charger.
For communication over secured connection both sides need synchronized clocks in order for certificates to be valid and secure connection, between backend and charger, can be established.
How to manually synchronize clock on charger:
Connect to charger interface with computer and open Settings menu.
Then go to Configuration
Click on Time and Regional settings
This will open submenu of Time and Timezone settings. If you want to synchronize time, click on button Synchronize time. This will synchronize time on charger with your computer time, or you can add your own NTP server in the field Time synchronization with Time (NTP) servers. Save settings and changes should be applied (Green pop-up will appear in upper right corner)
After successfully saving settings, you can reboot charger. After reboot, secure connection with backend should be working.