Serial Com to ProSim2 using Python

Question

I am trying to write a basic GUI in python to communicate with PromSim2 using the commands as listed in the [datasheet](from PDF page 40 onwards).

I am trying to use Python serial mode using the below functions.

def connect_dev():
    try:
        global access
        access=1       
        ser.flushOutput()
        time.sleep(2)
        ser.write(b'REMOTE\r\n')
        time.sleep(2)
        ser.flushOutput()
        time.sleep(2)
        ser.flushOutput()
        ser.write(b'QMODE\r\n')
        if ser.read(8)==b'':
            raise UnboundLocalError()
        else:
            status_label.config(text=f"Device in Remote access")
    except UnboundLocalError:
        status_label.config(text=f"Error! Connect to the COM port")
def BPM_set():
    selected_item_list1 = listbox1.get(listbox1.curselection())
    selected_item_list1_strip=selected_item_list1[:-3].rstrip()
    cmd='NSR'+selected_item_list1_strip
    # print(cmd)
    ser.flushOutput()
    #time.sleep(2)
    ser.write(b'{cmd}\r\n')    
    ser.flushOutput()
    time.sleep(2)
    print(ser.readline().decode("utf-8"))
    if selected_item_list1:
        # Perform specific function based on selected item from List 1
        print("Selected Item from List 1:", cmd)

Delay addition(sleep) to the function doesn't seem to help so have added couple of flush functions still not sure if anything else I am missing in the BPM_set() functions?

Now, If I want to set 30bpm(table-11) using TeraTerm tool with serial interface properties (port,baudrate=9600,bytesize=8, parity='N', stopbits=1, timeout=2,xonxoff=0) as defined in the datasheet I am able to configure the device. Using TeraTerm after estabilishing the COM connection, I enter REMOTE command and get RMAIN on screen then I enter NSR30 and get OK on the screen indicating the remote access and 30bpm setting successfully done.

Using the Python code 1.The connect_dev function works successfully --> device enters Remote access mode. 2.The BPM_set function which takes the 'NSR' and subsequent numerical value from a list and sends the cmd(the cmd value varies as NSR30) throws '?' or ERR01, UNKNOWN COMMAND.