Some users have encountered a transfer problem if the new iPhone updates iOS during the transfer.
If this is your case, stop the update and configure your iPhone as a new iPhone, i.e. without transferring data. This will allow you to update iOS.
To stop the update, force restart the iPhone:
- Press quickly the volume+ button.
- Press quickly the volume- button.
- Press and hold the side button until the Apple logo appears. It can take up to 20 seconds.
Configure the new iPhone as a "new" iPhone and update iOS. Once the update is done, erase the iPhone (Settings > General > Transfer or Reset iPhone and tap Erase Content and Settings) then configure it again, this time by transferring data with Quick Start.