How to wake from OFF mode with a GPIO pin on the nRF52810

Question

I have an nRF52810 on a custom board and can't get it to wake from System Off mode. The code: 
 nrf_gpio_cfg_sense_input(9, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);
sd_power_system_off(); 
 trying it with a different way to turn the system off also didn't work: 
 nrf_gpio_cfg_sense_input(9, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_SENSE_LOW);
nrf_pwr_mgmt_shutdown(NRF_PWR_MGMT_SHUTDOWN_GOTO_SYSOFF); 
 Both of these methods worked on the PCA10040 HDK, the pin is being driven by an external signal and that worked with an nRF52832. I have also tried to use pin 18 instead and that didn't work either. Does anybody know anything that could help?

CCD technics · Answer

Took a little while to figure out because manually triggering the wakeup with a wire didn't work. In the end the pull-up resistor was too large, switching to a 1.5k resistor did the trick.