Add FreeRTOS into serial example but nrf_serial_read() read string fail

Question

SDK version: nRF5_SDK_15.3.0 
 Platform: nRF52840 DK 
 --- 
 Add FreeRTOS into serial example( nRF5_SDK_15.3.0_59ac345\examples\peripheral\serial ) 
 and I copy task of blinky_freertos example into this project, it work. 
 int main(void)
{
 ret_code_t ret;

 ret = nrf_drv_clock_init();
 APP_ERROR_CHECK(ret);
 ret = nrf_drv_power_init(NULL);
 APP_ERROR_CHECK(ret);

 nrf_drv_clock_lfclk_request(NULL);
 ret = app_timer_init();
 APP_ERROR_CHECK(ret);

 // Initialize LEDs and buttons.
 bsp_board_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS);

#if 1
 /* Create task for LED0 blinking with priority set to 2 */
 UNUSED_VARIABLE(xTaskCreate(led_toggle_task_function, "LED0", configMINIMAL_STACK_SIZE + 200, NULL, 2, &led_toggle_task_handle));

 led_toggle_timer_handle = xTimerCreate( "LED1", TIMER_PERIOD, pdTRUE, NULL, led_toggle_timer_callback);
 UNUSED_VARIABLE(xTimerStart(led_toggle_timer_handle, 0));

 SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;

 vTaskStartScheduler();

 while (true)
 {
 /* FreeRTOS should not be here... FreeRTOS goes back to the start of stack
 * in vTaskStartScheduler function. */
 }
#endif

} 
 
 Then, add uarte into main(): it's don't work. 
 int main(void)
{
 ret_code_t ret;

 ret = nrf_drv_clock_init();
 APP_ERROR_CHECK(ret);
 ret = nrf_drv_power_init(NULL);
 APP_ERROR_CHECK(ret);

 nrf_drv_clock_lfclk_request(NULL);
 ret = app_timer_init();
 APP_ERROR_CHECK(ret);

 // Initialize LEDs and buttons.
 bsp_board_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS);

 ret = nrf_serial_init(&serial_uart, &m_uart0_drv_config, &serial_config);
 APP_ERROR_CHECK(ret);

 static char tx_message[] = "Hello Tim!
";

 ret = nrf_serial_write(&serial_uart,
 tx_message,
 strlen(tx_message),
 NULL,
 NRF_SERIAL_MAX_TIMEOUT);
 APP_ERROR_CHECK(ret);

 while (true)
 {
 char c;
 ret = nrf_serial_read(&serial_uart, &c, sizeof(c), NULL, 1000);
 if (ret != NRF_SUCCESS)
 {
 continue;
 }
 (void)nrf_serial_write(&serial_uart, &c, sizeof(c), NULL, 0);
 (void)nrf_serial_flush(&serial_uart, 0);

 }

#if 1
 /* Create task for LED0 blinking with priority set to 2 */
 UNUSED_VARIABLE(xTaskCreate(led_toggle_task_function, "LED0", configMINIMAL_STACK_SIZE + 200, NULL, 2, &led_toggle_task_handle));

 led_toggle_timer_handle = xTimerCreate( "LED1", TIMER_PERIOD, pdTRUE, NULL, led_toggle_timer_callback);
 UNUSED_VARIABLE(xTimerStart(led_toggle_timer_handle, 0));

 SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;

 vTaskStartScheduler();

 while (true)
 {
 /* FreeRTOS should not be here... FreeRTOS goes back to the start of stack
 * in vTaskStartScheduler function. */
 }
#endif

}
 
 I find that 
 In nrf_serial_read() call timeout_setup() to create timer (call app_timer_create()) 
 but the app_timer_create() return errorcode = 8 (Invalid state, operation disallowed in this state) 
 I not sure why errorcode=8, and how to fix? 
 
 and timer create fail 
 
 BTW, I include app_timer_freertos.c instead of app_timer.c, and use RTC1. 
 https://drive.google.com/file/d/1LnsNW1LME_fONC2Wyhs8Pjsr-679NLJJ/view 
 
 Thanks, 
 Tim