cannot get P0.09 to operate as a GPIO

I've tried everything I can find on this topic and I still cannot get P0.09 to behave as a GPIO pin. Does it have something to do with the way I'm attempting to initialize the pin (see below)? If so, what are the constraints on this pin as a GPIO?

nrf_drv_gpiote_in_config_t config = GPIOTE_CONFIG_IN_SENSE_HITOLO(false);
// Macro does not set the pullup or pulldown
config.pull = NRF_GPIO_PIN_PULLUP;
err_code = nrf_drv_gpiote_in_init(HESA_TOP_PIN_NUMBER, &config, hesa_pin_event_handler);
APP_ERROR_CHECK(err_code);
nrf_drv_gpiote_in_event_enable(HESA_TOP_PIN_NUMBER, false);