My school kid has a quite usable “mechanical” phone (designed for elderly people, with emergency calls, it’s part of their emergency kit) but it has a hardcored number of possible characters for a voucher of 12 digits. All vouchers we had so far have 16 digits… 🤨

[a photo of the phone: it’s a high contrast bar shaped phone with basically four preset numbers as mechanical keys and no number pad, the screen shows that 12 digits are expected]