The Series 4 units were sending power as a string. "value": "14.4kW" . The OCPP 2.0.1 schema demanded a float. "value": 14.4 .
If you need a , pinout , or API documentation for a particular OCPP-809 hardware module, please provide: ocpp-809 driver
If you cannot find the specific manufacturer driver, a generic ESC/POS driver can often handle basic text and receipt printing. Installation Guide Cheap 80mm Pos Thermal Printer with auto cutter(OCPP-809) The Series 4 units were sending power as a string
Visit the OCOM Download Center or the specific OCPP-809 Product Page . ocpp-809 driver
Assuming you have a Linux-based gateway (Debian/Ubuntu) and an 809 board connected via /dev/ttyUSB0 :