Are you using a lap top? The word Firefox suggested that. It is easier than the phone app. Are you using photos at least 1024px X 63px?
Are you using horizontal instead of vertical when taking pictures? These tips helped me. If you go into AirBnB Community Center multiple people have had this happen & over 60 answers.
As @Bettye6 mentions, the usual culprit is the pictures must be at least 1024x683 pixels, or the photos are not accepted. If you are trying to upload from a phone, this could also be the issue. Phones will reduce the quality (pixels) of photos to allow for more storage on a phone. So if someone texts you photos, they will be a lower quality.
It's best to email the photos to yourself and download them on a computer. Then upload to your listing from a computer.