Sending Data from Arduino to PixHawk using Mavlink

Hello.
I have this issue with sending data from Arduino to PixHawk.

Basically, I have connected both components through Rx and Tx pins. As shown in the figure below.

I also have this arduino code where it can send mavlink messages to the pixhawk with the specific baudrate set.

#include <mavlink.h>

void setup() {
  Serial.begin(57600);
}

void loop() {
  int data = 132;
  
  uint32_t now = millis();
  mavlink_message_t msg;
  mavlink_msg_heartbeat_pack(1, 200, &msg, MAV_TYPE_GENERIC, MAV_AUTOPILOT_INVALID, MAV_MODE_PREFLIGHT, 0, MAV_STATE_STANDBY);
  uint8_t buf[MAVLINK_MAX_PACKET_LEN];
  uint16_t len = mavlink_msg_to_send_buffer(buf, &msg);
  Serial.write(buf, len);
  delay(1000);
}

My only issue here is how can I manipulate this arduino code so that it can send basic data to the pixhawk like a simple 123 or “Hello”?
I’ve been trying to manipulate it but it doesn’t seem to work. Or is it possible at all? Thanks!

Hello,

Did you solve the problem?