We’ve been helping a client today resetting their iPhone 7 and encountered the error “The iPhone “iPhone” could not be restored. An unknown error occurred (3503)”.
Initially we thought there might be an issue with the Windows machine we were restoring it from or iTunes, however we’ve now tried 3 different laptops and all encounter the same error.
Here is a screenshot of the issue:
We believe this may be an Apple server issue with the Windows version of iTunes.
We can confirm that following the exact same process on an iMac has worked successfully today, as shown on the images:
We are awaiting a response from Apple regarding the issue. If anyone has found a workaround for Windows for the issue, we’d love to know so we can update this page.