Reading L&T ER300P based on DLMS Protocol

Question

I am trying to read an energy meter via a customized development board. I can successfully read data from the meter using the serial terminal software (Hterm) but unable to read the same using my customized development board. Following are the details of the energy meter: Make and model: L&T ER300P Communication Protocol: DLMS(IS15959-Indian standard) Communication Port: RJ-11 over RS232 Serial settings of the meter: Baud Rate-9600,Parity-None,Stop bits:1

The meter basically works in request response method. Using the serial terminal software (Hterm), I get the response from the meter properly. Following methodology is used while reading data from the serial terminal. 1. Connecting meter to the PC using combination of RJ-11-DB-9 and (DB-9 Serial to USB Cable) 2. Assert RTS in terminal software before sending data (Screenshot attached for reference). Voltage at the shorted RTS/CTS line: 4.95 volts 3. Send the request frame in Hexadecimal format- (Meter will respond)

While Connecting Dev Board and Meter directly, following methodology is used 1. RTS line made Low(Zero) Voltage at the shorted RTS/CTS line: 6.63 volts 2. Send the hexadecimal frame- But no response is received. 3. I have checked the serial DB-9 Port of the Dev board and it works fine using same firmware for other make meters. 4. Serial settings in Dev board are also fine as the same Dev board can access other devices. Details of the Dev board: Micro-controller Used: MSP430

I think i am making some mistake at handling RTS/CTS lines in my firmware. Any input on how these RTS/CTS lines should be handled- Can the voltage levels which are a bit higher for dev board at DB-9 RTS/CTS pins(6.63) are causing any problem ? The vendor has advised to short RTS-CTS and DTR-DSR pins at the DB-9 end. I have also attached connection diagram shared by the vendor for reference. enter image description hereenter image description here