Use the manual details on the same order page instead. They install exactly the same eSIM and do not need a camera.
If you are scanning from the phone that is displaying the code, that is the problem: screenshot the code and pick the picture from your photos when asked to scan.
A code that was already scanned once cannot be scanned again. If the eSIM is already on a phone, it is installed and there is nothing more to do.
Brightness helps too — turn the screen showing the code up, and hold the phones a little further apart.