Initializing connection parameters fail

[Artucas]

Helo, i'm working on firmware for a device, which should be able to scan for other devices, advertise data and be connectable. Scanning and advertising works. Problems come up when i tried to add code to make device connectable as well. This configuration fails in app_error_handler with error_code 0x00000008, which i can see means NRF_ERROR_INVALID_STATE. Could you guys can help me figure out what is causing this? Im posting my main.c code also.

static void conn_params_init(void)
{
    uint32_t               err_code;
    ble_conn_params_init_t cp_init;

    memset(&cp_init, 0, sizeof(cp_init));

    cp_init.p_conn_params                  = NULL;
    cp_init.first_conn_params_update_delay = FIRST_CONN_PARAMS_UPDATE_DELAY;
    cp_init.next_conn_params_update_delay  = NEXT_CONN_PARAMS_UPDATE_DELAY;
    cp_init.max_conn_params_update_count   = MAX_CONN_PARAMS_UPDATE_COUNT;
    cp_init.start_on_notify_cccd_handle    = BLE_GATT_HANDLE_INVALID;
    cp_init.disconnect_on_fail             = false;
    cp_init.evt_handler                    = on_conn_params_evt;
    cp_init.error_handler                  = conn_params_error_handler;

    err_code = ble_conn_params_init(&cp_init);
    APP_ERROR_CHECK(err_code);
}

and my main looks like this:

    bool erase_bonds;
    ble_stack_init();

    application_data_flash_manager_init();
    
    /* Get identifier of block of flash which is used for R/W operations */
    pstorage_block_identifier_get(&handle, 0, &block_0_handle);
    pstorage_load(flash_block0_data, &block_0_handle, 16, 0);

    application_adc_init();
    
    /* Measure battery level */
    battery_adc_value = measure_battery_level();

   /* Putting data in advertisement buffer here */
   // .....

    client_handling_init();
    device_manager_init(erase_bonds);

    gap_params_init();
    services_init();
    advertising_init(); 
    conn_params_init();

    /* Start atvertising */
    advertising_start();

[RK]

Where does it fail? The APP_ERROR_CHECK() in the conn params init function or somewhere else? Have you single-stepped into the ble_conn_params_init() function to see which of the calls is returning the error? I don't see anything in the code for ble_conn_params_init() which can return that invalid state error, so perhaps it's coming from elsewhere.

And what softdevice and version?