| separates a rule. So
digits_between|min:1|max:3 is 3 rules, the first being incorrectly formatted.
The docs say
digits_between is formatted like
digits_between:min,max. The min and max parts must be replaced with a number.
So I think what you were trying to do was
digits_between:1,3|min:1|max:3 would mean "a number with 1 to 3 digits AND from 1 to 3", which basically renders the
digits_between part useless (possible values would be 1, 2 and 3 only).
If you're trying to allow ages from 1 to 100 year (for example), the easiest would be to just use