Feedback-"Click"?

Hello,

according to https://docs.lvgl.io/latest/en/html/porting/indev.html, I’m trying to install a feedback-callback which gives me a “Click” whenever the touchpad is touched:

    /* initialize input device */
    lv_indev_drv_init (&touch_indev_drv);
    touch_indev_drv.type = LV_INDEV_TYPE_POINTER;
    touch_indev_drv.read_cb = LVGL_Touch_Read_Callback;
    touch_indev_drv.feedback_cb = audio_play_click;

    touch_indev = lv_indev_drv_register (&touch_indev_drv);

But the callback is never called at all.

What am I missing here?