That means that your device is not able to track the floor significantly to place a Space in reality. Try to get more light in your room. Or find a spot so that there is more contrast in the picture. Your device will then be able to track depth and subsequently track the floor.
Here is a video to explain how Fectar works:
If your device is still not able to find the floor, you will be offered the option to view the Space in a Virtual Room on your device.