ESP32 or ESP8266 sender

esp32_sendTo_com4_numbers.ino

/*
 * SerialOutput sketch
 * Print numbers to the serial port
 vezi php_receive.php
*/
void setup()
{
  Serial.begin(9600); // send and receive at 9600 baud
}

int number = 0;

void loop()
{
  Serial.print("The number is ");
  Serial.println(number);    // print the number

  delay(500); // delay half second between numbers
  number++; // to the next number
}

you also can test if program working using Putty serial with following parameter:
port=COM4(for windows) and
speed=9600