Hi @jkandasa and thanks a lot for your answer!

Here is my gateway sketch:

// Enable debug prints to serial monitor
#define MY_DEBUG

// Enable and select radio type attached
#define MY_RADIO_RFM69
#define MY_IS_RFM69HW
#define MY_RFM69_FREQUENCY (RFM69_868MHZ)

// Enable serial gateway
#define MY_GATEWAY_SERIAL

#include <MySensors.h>

void setup()
{
        // Setup locally attached sensors
}

void presentation()
{
        // Present locally attached sensors
}

void loop()
{
        // Send locally attached sensor data here
}

I enabled MY_DEBUG but it may be a mistake and the cause of the problem. I'll try without!

I got it for the button part, everything looks ok for my dummy node, thanks!