Can't get my M5 Core Ink to wake up from deep sleep using a button :

esp_sleep_enable_ext0_wakeup(GPIO_NUM_5, LOW); // EXT buton
esp_deep_sleep_start();

It goes to deep sleep but does not wake up from button. It does wake up from an RTC timer though.
I also tried holding power pin without success:

gpio_hold_en((gpio_num_t) POWER_HOLD_PIN);
gpio_deep_sleep_hold_en();

Thanks for your help!
Alex.