@Override
    public boolean isSubscribeSupported() {
        Plc4xProtocolBase<?> protocol = getProtocol();
        S7DriverContext s7driverContext = (S7DriverContext) protocol.getDriverContext();
        return (s7driverContext.getControllerType() == ControllerType.S7_300) || (s7driverContext.getControllerType() == ControllerType.S7_400);
    }
Subscriptions are only supported in a small subset of the S7 devices.

@return true, if the device supports subscriptions.
plc4j/drivers/s7/src/main/java/org/apache/plc4x/java/s7/readwrite/protocol/S7HPlcConnection.java