See the information for the Redflow ZCell at https://www.victronenergy.com/live/battery_compatibility:redflow_zcell
Redflow ZBM batteries can be directly interfaced to the GX device (Cerbo GX) for monitoring and control (see below).
Alternatively one or more ZBM batteries can be used with the Redflow/ZCell Battery Management System (BMS). That results in keeping all ZBM specific information and control inside the BMS and sending only general summary data (such as system State of Charge) up to the GX device using a TCP/IP connection. See the Redflow ZCell page at the link above for more information.
For the direct-attach option, the GX device has built in support for directly attaching to one or more Redflow ZBM batteries using the built in Modbus connection and protocol.