Sending Pulse rate via 433mhz rf

Hello goo day, I need some help receiving values from my transmitter,
It show my pulse rate sensor to my serial monitor if it is String, but broken or square icon if i try to send int.

RECEIVER:

#include <RH_ASK.h>
#include <SPI.h> // Not actualy used but needed to compile

 RH_ASK driver(2000, 2, 9, 10); // ESP8266: do not use pin 11

void setup()
{
    Serial.begin(9600);	// Debugging only
    if (!driver.init())
         Serial.println("init failed");
}

void loop()
{
    uint8_t buf[RH_ASK_MAX_MESSAGE_LEN];
    uint8_t buflen = sizeof(buf);

    if (driver.recv(buf, &buflen)) // Non-blocking
    {
	int i;

	String str= "";
  for(int i = 0; i <buflen; i++){
  str += (char)buf[i];
 
 }
  Serial.println(str);
    }
}
TRANSMITTER:

#include <RH_ASK.h>

///////TEST
int BPM = 0;
int BPMdata;

//////

RH_ASK driver(2000, 9, 2, 5); // ESP8266: do not use pin 11

void setup()
{  //// 

  ////TEST
    Serial.begin(9600);	  // Debugging only
    if (!driver.init())
    Serial.println("init failed");
}

void loop()
{
   BPMdata = analogRead(BPM);  // Read the PulseSensor's value. 
                                              // Assign this value to the "Signal" variable.

   Serial.println(BPMdata); 
  char  msg = BPMdata;
    
    driver.send((uint8_t *)msg, strlen(msg));
    driver.waitPacketSent();
    delay(200);


  
    
}

thanks

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