using Serial.print in a ticker object

Projects Programming
1

Hey,

I'm using a ESP32 board with the android IDE.

I get weird Serial print things when using the ticker object.

This is my code:

#include <Arduino.h>
#include <Ticker.h>

#define GREENLED 17
#define REDLED 19

Ticker tkrRedLed;
Ticker tkrGreenLed;

void flipPIN(int led) {
  digitalWrite(led, !digitalRead(led));
  Serial.println("changed LED #" + led);
}

void initiateLED(int led)
{
   pinMode(led, OUTPUT); 
   digitalWrite(led, LOW);
}

void setup() {
  Serial.begin(9600);
  Serial.println("start program");
  initiateLED(GREENLED);
  initiateLED(REDLED);

  tkrRedLed.attach_ms(1000, flipPIN, REDLED);
  tkrGreenLed.attach_ms(2000, flipPIN, GREENLED);
}

void loop() {
 
}

In the Serial monitor i get:

start program
 program
 program
rt program
 program
 program
rt program
 program
 program
rt program
 program
 program
rt program
 program
 program
rt program

Anybody knows what the problem is? Does Serial.print not work in a function passed to a ticker object?

thx^2