Unable to download params from pixhawk cube to raspberry pi 4B

I am trying to connect to pixhawk Cube with Raspberry Pi 4B. I have connected the UART pins of RPi to Pixhawk telem 2 port and set the baud rate to 921 in Mission Planner. I have also downloaded mavlink and mavproxy. I am able to connect over UART and get a heartbeat. However, I am unable to download params and send commands to control the pixhawk.
Please help.