Please revew the documentatuon here: https://api4.ai/docs/face-analysis
One of returened parameters is “results[].entities[].objects[].entities[name=face].classes.face”, it identifies face detection confidence. In case the API doesn’t return even a face with low confidence maybe this face is visible too bad.
To investigate the issue in more details plese send a couple of examples illustraing the problem at hello@api4.ai