I2C comunication, ESP->Nano on endTransmission no ACK fron nano i am trying to communicate between ESP(master) and arduino nano(slave). This is only a prototype and all works fine. But i want to  add multiple arduinos and therefor i need to detect if the arduino is connected.
I use the return function from wire.endTransmission as shown in i2c scanner to detect devices. But it doesnt work.
On the arduino i have this program:
#include &lt;Wire.h&gt;

const int16_t I2C_SLAVE = 0x22; // 0x22 = 34 cize izba 3(30)

void setup() {
  Wire.begin(I2C_SLAVE);  

}

void loop() {
  // put your main code here, to run repeatedly:

}

on the ESP i am trying this:
Wire.beginTransmission(I2C_adress[adress]);
int error = Wire.endTransmission();

Serial.println(error);

It returns only 2 (received NACK on transmit of address)
Why? When i have other code on the slave (with onRecive and onRequest all works and comunicates)
Thank you.
I'm a fool, I tried to detect other devices in the setup function before the Wire.begin(PIN_SDA, PIN_SCL,  I2C_MASTER);
I Found it only because of you. The rubber duck. I started to write the program down to post it here and bingo.
That was the reason why the master had the &quot;NACK&quot; answer. The master was not started yet.
Thank you