Troubles with serial connection between Core2 and AtomMatrix

[HappyUser]

Wow, this should have been simple but apparently I am overseeing something.
I have a M5Stack Core 2 connected to M5AtomMatrix using the Port A on Core 2 and HY2.0-4P port on the Matrix. Included the code of sender and receiver. But I dont see any transmission going on. Which obvious mistake am I making here?
M5Stack Core 2 code :

#include <M5Core2.h>
#include <Wire.h>
#define I2C_DEV_ADDR 0x55
uint32_t i = 0;

void setup() {

M5.begin(true, true, true, true);
delay(300);

Serial.setDebugOutput(true);
Wire.begin(32,33);  // SDA SCL M5Stack Core 2

}

void loop() {
delay(5000);

//Write message to the slave
Wire.beginTransmission(I2C_DEV_ADDR);
Wire.printf("Hello World! %u", i++);
uint8_t error = Wire.endTransmission(true);
Serial.printf("endTransmission: %u\n", error);

//Read 16 bytes from the slave
error = Wire.requestFrom(I2C_DEV_ADDR, 16);
Serial.printf("requestFrom: %u\n", error);
if(error){
uint8_t temp[error];
Wire.readBytes(temp, error);
log_print_buf(temp, error);
}

}

M5Atom Matrix code here:

//#include "M5Atom.h"
#include "M5StickC.h"
#include <Wire.h>
#define I2C_DEV_ADDR 0x55

uint32_t i = 0;

void onRequest(){
Wire.print(i++);
Wire.print(" Packets.");
Serial.println("onRequest");
}

void onReceive(int len){
Serial.printf("onReceive[%d]: ", len);
while(Wire.available()){
Serial.write(Wire.read());
}
Serial.println();
}

void setup() {

M5.begin(true,true,true);
delay(300);

Serial.begin(115200);
Serial.setDebugOutput(true);
Wire.onReceive(onReceive);
Wire.onRequest(onRequest);
Wire.begin(26,32); // SDA SCL M5Atom

}

void loop() {

}

[felmue]

Hello @HappyUser

you are so close. Right now you are setting up both devices as I2C masters. However M5Atom needs to be an I2C slave. To do this the first parameter of Wire.begin() needs to be the slave address. Try this:

Wire.begin((uint8_t)I2C_DEV_ADDR, 26, 32);

Thanks
Felix