Using Matlab as client for Bronkhorst FlowDDE

I have to write an application with Matlab, to control a FlowBus system, using RS232 standard serial communication. I tried to communicate directly to the system sending an ASCII string, following the instruction manual, for example to set the setpoint of a flowmeter, but it didn't work. The input is not received by the system, and it doesn't send back any string. I would like to know if there's any example of communication with similar systems written in Matlab, and if it is possible and easier to communicate with the FlowDDE server given by Bronkhorst, instead of using direct communication, and how this can be made. The code i wrote to test the communication is attached.