Problem with Async UART Example from peripheral_uart

[NautDesigner]

Trying to integrate the serial part of the example code for use with a custom nRF52840 board. The problem is that I'm getting an error in uart_callback_set(uart, uart_cb, NULL) that is causing "Cannot initialize UART callback" to be displayed. I'm using UART1 which works with a different interrupt version of this code. Not sure what I'm missing here to get the callback initialized.

int initUart() {
int err;
int pos;
struct uart_data_t *rx;
struct uart_data_t *tx;

   //fifoInit();
   uart = device_get_binding("UART_1");
	__ASSERT(uart, "Failed to get UART device");
	//interrupt_driven(uart);

	if (!uart) {
		return -ENXIO;
	}

	rx = k_malloc(sizeof(*rx));
	if (rx) {
		rx->len = 0;
	} else {
		return -ENOMEM;
	}

	k_work_init_delayable(&uart_work, uart_work_handler);

	err = uart_callback_set(uart, uart_cb, NULL);
	if (err) {
		LOG_ERR("Cannot initialize UART callback");
		return err;
	}

CONFIG_STDOUT_CONSOLE=n
CONFIG_UART_CONSOLE=n
CONFIG_NRF_SW_LPUART=n
CONFIG_NRF_SW_LPUART_INT_DRIVEN=y

# UART
CONFIG_SERIAL=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_LINE_CTRL=n
CONFIG_UART_ASYNC_API=y
CONFIG_UART_0_ASYNC=y
CONFIG_UART_1_ASYNC=y
CONFIG_UART_0_NRF_HW_ASYNC=y
CONFIG_UART_1_NRF_HW_ASYNC=y
CONFIG_UART_0_NRF_HW_ASYNC_TIMER=1
CONFIG_UART_1_NRF_HW_ASYNC_TIMER=2
CONFIG_NRFX_UARTE=y
CONFIG_NRFX_UARTE0=y
CONFIG_NRFX_UARTE1=y
CONFIG_NRFX_TIMER=y
CONFIG_NRFX_TIMER1=y
CONFIG_NRFX_TIMER2=y
CONFIG_NRFX_PPI=y
CONFIG_NRFX_TIMER2=y

[NautDesigner]

Here is the callback code.

static void uart_cb(const struct device *dev, struct uart_event *evt, void *user_data)
{
	ARG_UNUSED(dev);

	static uint8_t *current_buf;
	static size_t aborted_len;
	static bool buf_release;
	struct uart_data_t *buf;
	static uint8_t *aborted_buf;

	switch (evt->type) {
	case UART_TX_DONE:
		LOG_DBG("tx_done");
		if ((evt->data.tx.len == 0) ||
		    (!evt->data.tx.buf)) {
			return;
		}

		if (aborted_buf) {
			buf = CONTAINER_OF(aborted_buf, struct uart_data_t,
					   data);
			aborted_buf = NULL;
			aborted_len = 0;
		} else {
			buf = CONTAINER_OF(evt->data.tx.buf, struct uart_data_t,
					   data);
		}

		k_free(buf);

		buf = k_fifo_get(&fifo_uart_tx_data, K_NO_WAIT);
		if (!buf) {
			return;
		}

		if (uart_tx(uart, buf->data, buf->len, SYS_FOREVER_MS)) {
			LOG_WRN("Failed to send data over UART");
		}

		break;

	case UART_RX_RDY:
		LOG_DBG("rx_rdy");
		buf = CONTAINER_OF(evt->data.rx.buf, struct uart_data_t, data);
		buf->len += evt->data.rx.len;
		buf_release = false;

		if (buf->len == UART_BUF_SIZE) {
			k_fifo_put(&fifo_uart_rx_data, buf);
		} else if ((evt->data.rx.buf[buf->len - 1] == '\n') ||
			  (evt->data.rx.buf[buf->len - 1] == '\r')) {
			k_fifo_put(&fifo_uart_rx_data, buf);
			current_buf = evt->data.rx.buf;
			buf_release = true;
			uart_rx_disable(uart);
		}

		break;

	case UART_RX_DISABLED:
		LOG_DBG("rx_disabled");
		buf = k_malloc(sizeof(*buf));
		if (buf) {
			buf->len = 0;
		} else {
			LOG_WRN("Not able to allocate UART receive buffer");
			k_work_reschedule(&uart_work, UART_WAIT_FOR_BUF_DELAY);
			return;
		}

		uart_rx_enable(uart, buf->data, sizeof(buf->data),
			       UART_WAIT_FOR_RX);

		break;

	case UART_RX_BUF_REQUEST:
		LOG_DBG("rx_buf_request");
		buf = k_malloc(sizeof(*buf));
		if (buf) {
			buf->len = 0;
			uart_rx_buf_rsp(uart, buf->data, sizeof(buf->data));
		} else {
			LOG_WRN("Not able to allocate UART receive buffer");
		}

		break;

	case UART_RX_BUF_RELEASED:
		LOG_DBG("rx_buf_released");
		buf = CONTAINER_OF(evt->data.rx_buf.buf, struct uart_data_t,
				   data);
		if (buf_release && (current_buf != evt->data.rx_buf.buf)) {
			k_free(buf);
			buf_release = false;
			current_buf = NULL;
		}

		break;

	case UART_TX_ABORTED:
			LOG_DBG("tx_aborted");
			if (!aborted_buf) {
				aborted_buf = (uint8_t *)evt->data.tx.buf;
			}

			aborted_len += evt->data.tx.len;
			buf = CONTAINER_OF(aborted_buf, struct uart_data_t,
					   data);

			uart_tx(uart, &buf->data[aborted_len],
				buf->len - aborted_len, SYS_FOREVER_MS);

		break;

	default:
		break;
	}
}