I can feel the pain when you are stuck on the last page or final steps. This could be a permissions problem. like due to security reasons certain apps don't allow screenshot, same could be the permissions problem.
Here is what to do -
Open Settings > Apps > Camera Apps and allow all permissions.
Also, open Settings > Apps > app where you are uploading photos and allow all permissions.
Here is the guide for app permissions Android: https://support.google.com/android/answer/9431959?hl=en
Alternatively, install any other camera app on your phone and use it.
If I am still not clear, please let me know the app name.
Also contact the customer care agent, they will help you better or visit nearest store.