HI Anoop R Nair
I have no issue if I place the code below code in the echo demo from the SDK version 3.0.0:
LPUART_DRV_SendData(INST_LPUART1, buffer, bufferIdx);
while(LPUART_DRV_GetTransmitStatus(INST_LPUART1, &bytesRemaining) != STATUS_SUCCESS);
If you are using the EVK board, you should be using the LPUART1 instance, could you clarify why in the code that you attached you are using instance 2?