Why an encrypted config backup breaks when you move servers — and how I fixed it in laravel-config-backup

Imagine you write a letter in a secret code that only your old house key can read. Then you move. You photocopy the coded letter, carry it to the new house… and realise the new key can't decode any of it. The letter is valid, just useless. That's effectively what happens when you back up encrypted values from a Laravel database and restore them onto a different server. I hit exactly this while working on laravel-config-backup today, so here's the problem and the fix. The real cause: C