Understanding the working of ESP-NOW library

#include <WifiEspNow.h>
#if defined(ESP8266)
#include <ESP8266WiFi.h>
#elif defined(ESP32)
#include <WiFi.h>
#endif
#define ONBOARD_LED  2
#define BUTTON1   36 //pin D5

int buttonState = 0;         // current state of the button
int lastButtonState = 1;     // previous state of the button

//MAC address of this node is 10:52:1C:52:0A:C5
//30:AE:A4:97:B4:CD

//static uint8_t PEER[] {0x30, 0xAE, 0xA4, 0x97, 0xDB, 0x05};
//char string_var[10];

static uint8_t PEER[] {0x10, 0x52, 0x1C, 0x52, 0x0A, 0xC5};

void printReceivedMessage(const uint8_t mac[6], const uint8_t* buf, size_t count, void* cbarg) {
  char string_var[100];
  Serial.printf("Message from %02X:%02X:%02X:%02X:%02X:%02X\n", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
  for (int i = 0; i < count; ++i) {
    Serial.println(static_cast<char>(buf[i]));
  }

    size_t bufflen = sizeof(buf)+1;
    memcpy( string_var, buf, bufflen );
    string_var[bufflen] = '\0'; // 'str' is now a string
    Serial.print("string_var=");
    Serial.println(string_var);
  strcpy(
  //strcat(string_var, (char*)buf);
  //Serial.print("string_var=");
  //Serial.println(string_var);
 
  if (strncmp(string_var, "ok",2) == 0){
    digitalWrite(ONBOARD_LED,HIGH);
  }
  if (strncmp(string_var, "reset",5) == 0){
    digitalWrite(ONBOARD_LED,LOW);
  }
  Serial.println();
}







void setup() {
  pinMode(ONBOARD_LED,OUTPUT);
  pinMode(BUTTON1,INPUT);
  Serial.begin(115200);
  Serial.println();
 
 
  WiFi.persistent(false);
  WiFi.mode(WIFI_AP);
  WiFi.softAP("ESPNOW", nullptr, 3);
  WiFi.softAPdisconnect(false);
  Serial.print("MAC address of this node is ");
  Serial.println(WiFi.softAPmacAddress());

  bool ok = WifiEspNow.begin();
  if (!ok) {
    Serial.println("WifiEspNow.begin() failed");
    ESP.restart();
  }

  WifiEspNow.onReceive(printReceivedMessage, nullptr);

  ok = WifiEspNow.addPeer(PEER);
  if (!ok) {
    Serial.println("WifiEspNow.addPeer() failed");
    ESP.restart();
  }
}

void loop() {
  check_button_state(BUTTON1);
  //char msg[60];
  //int len = snprintf(msg, sizeof(msg), "hello ESP-NOW from %s at %lu", WiFi.softAPmacAddress().c_str(), millis());
  //WifiEspNow.send(PEER, reinterpret_cast<const uint8_t*>(msg), len);
  delay(100);
}



void check_button_state(int pin){

  buttonState = digitalRead(pin);
  if (buttonState != lastButtonState) {
    if (buttonState == HIGH){
      char msg[60];
      int len = snprintf(msg, sizeof(msg), "2");
      WifiEspNow.send(PEER, reinterpret_cast<const uint8_t*>(msg),len);
      // if the current state is HIGH then the button went from off to on:
      Serial.println("on");
    }
      else {
      // if the current state is LOW then the button went from on to off:
      Serial.println("off");
    }
  }
  lastButtonState = buttonState; 
}