MKR1300 does not wake up

Hi Everybody,

I have an Arduino MKR 1300 WAN which I want to put in deep sleep mode.
The program starts the deep sleep, but never wakes up?
Do I have to connect the reset pin to a GPIO?

My simple sample program. Commenting out LowPower.attachInterruptWakeup does not change anything.

Thanks for any help
Charly

#include "ArduinoLowPower.h"

void dummy()
{
  Serial.println("dummy");
}

void setup()
{
  // put your setup code here, to run once:
  Serial.begin(115200);
  while (!Serial)
    ;
  Serial.println("setup");
  pinMode(LED_BUILTIN, OUTPUT);
  // Uncomment this function if you wish to attach function dummy when RTC wakes up the chip
  LowPower.attachInterruptWakeup(RTC_ALARM_WAKEUP, dummy, CHANGE);
}

void loop()
{
  Serial.println("loop");
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
  // Triggers a 2000 ms sleep (the device will be woken up only by the registered wakeup sources and by internal RTC)
  // The power consumption of the chip will drop consistently
  LowPower.sleep(2000);
}