Photo formats accepted by the site are the universal jpg (also jpeg) and png formats. Some newer phones take photos in either heic or webp formats which can't be displayed by web browsers yet. The website has a filter so that these photos that can't be displayed cannot be uploaded. Some phones, however, will allow you to upload those formats anyway. If you do, you'll see blank photos on your listing. The best solution is to still take photos in jpg format. Every phone has a camera setting to take photos in this format, often called most compatible, meaning that the photos can be freely transferred between devices. If you already have heic or webp photos and want to change them to jpg, there are free numerous online websites which do this. Search for free online heic to jpg or similar.