ESPNOW_ESP32 Sender Example from https://www.youtube.com/watch?v=Ydi0M3Xd_vs

slim-owl-tx.ino

#include <esp_now.h>
#include <WiFi.h>

#define CHANNEL 1

/** This is all the data about the peer **/
esp_now_peer_info_t slave;

/** The all importent data **/ 
uint8_t data = 0;

void setup()
{
  Serial.begin(11520);
  WiFi.mode(WIFI_STA);
  esp_now_init();
  esp_now_register_send_cb(onDataSent);
  ScanForSlave(); // WiFi.mocAddress()
  esp_now_add_peer(&slave);
}

void loop()
{

  esp_now_send(slave.peer_addr, &data, sizeof(data));
  data++;
  delay(3000);
}


/** Scan for slaves in AP mode and ad as peer if found **/
void ScanForSlave()
{
  uint8_t scanResults = WiFi.scanNetworks();

  for (int i = 0; i < scanResults; ++i)
  {
    String SSID = WiFi.SSID(i);
    String BSSIDstr = WiFi.BSSIDstr(i);

    if (SSID.indexOf("RX") == 0)
    {

      int mac[6];
      if (6 == sscanf(BSSIDstr.c_str(), "%x:%x:%x:%x:%x:%x", &mac[0], &mac[1], &mac[2], &mac[3], &mac[4], &mac[5]))
      {
        for (int ii = 0; ii < 6; ++ii)
        {
          slave.peer_addr[ii] = (uint8_t)mac[ii];
        }
      }

      slave.channel = CHANNEL; // pick a channel
      slave.encrypt = 0;     // no encryption
      break;
    }
  }
}

/** callback when data is send from Master to Slave **/
void onDataSent(const uint8_t *mac_addr, esp_now_send_status_t status)
{
  Serial.print("I sent my data -> ");
  Serial.println(data);
}