Your device settings may have insufficient access permissions for "Photos" or "Storage" for Teachme Biz.
Please check the following according to your device.
▼Granting Camera, Image, and Video Access to Teachme Biz (iOS version)
https://teachme.jp/8/manuals/31654649
▼Granting Teachme Biz Access to Device Camera, Images, and Videos (Android Version)
https://teachme.jp/8/manuals/31794055