Cannot fully erase text field's content to enter new values

Say I want to enter the value 2 in the field below. Pressing “backspace” (to then type 2) doesn’t work. Instead, I need to move my cursor before the 0, type 2, move my cursor after the zero, then press backspace. I understand this behavior is a nice shortcut to avoid the need for developing error messages, but perhaps a more intuitive option that still doesn’t require new UI development is to allow the user to type anything they like but to not save their input if it is invalid. (Of course, error messages would be best, time permitting.)