done. Wrong images as input
Pix4Dmapper is an image processing software that is based on automatically finding thousands of common points between images. Each characteristic point found in an image is called a keypoint. When 2 keypoints on 2 different images are found to be the same, they are matched keypoints . Each group of correctly matched keypoints will generate one 3D point. When there is high overlap between 2 images, the common area captured is larger and more keypoints can be matched together. The more keypoints there are, the more accurately 3D points can be computed. Therefore, the main rule is to maintain high overlap between the images .
In your case the flight plan you followed is not optimal as not a lot of keypoints can be extracted since there was low overlap. Please have a look at the article below as the image acquisition plan has a high impact on the quality of the results, it is important to design it carefully. I would also suggest flying higher if possible. In most cases, flying higher improves the results.