I have a Classic form in Nintex for O365 that the user has decided now needs to be validated as 4-6 digits.

I have set the single line text field to validate using Regular Expression: ^\d{4,6}$

In testing in preview it doesn’t matter whether I type in a 4 digit number or 4 letters it still gives the validation error.

I have never used regular expression validation before so not sure if I am doing this right.

NOTE: I tested using a Test New Responsive form and it worked.  Unfortunately, I cannot get it to work for this Class Form.  I am in the middle of migrating all forms to New Responsive but this one hasn’t been done yet. 

Thanks for your help!