[Answered ]-Regex validator does not work with Django admin forms

Your current regex checks that your value contains a single character from a-z. So it allows a, but it also allows a1.

Try changing the regex to:

regex=r"^[a-z]+$"

By including ^ and $ to mark the beginning and end of string, you make sure that your string contains only characters from a-z. The + allows multiple characters.