How to validate a form field to accept exactly 4 numbers

A field, e.g. 4Numbers, that only validates when the input is exactly 4 digits.

We want to mark a form as valid only if the input is exactly 4 digits

Any other input should be marked as invalid.

Under the Field Validation Rules tab for your field, mark form as Valid without message when:

data["4Numbers"]=~"^[0-9]{4}$"

This regex checks that:

Add an "Otherwise" condition to catch anything that doesn't match and mark it invalid:

1==1

This always evaluates as true, meaning any unmatched input is invalid by default.

If you need a form field to accept exactly four numeric digits, this guide walks you through configuring that with a regex validation rule in Flow.