Hi @omezquita 

Since your are completely new to Nintex Forms, suggest that you watch this basic tutorial for Nintex Classic Form.

First off, which forms designer are you using (Responsive or Classic)? In my example, I’m using the Responsive Designer.

I was able to get this working on my end using these steps:

1. Add and configure form controls on the form for Date1 and Date2. Set “Date only” control configuration to Yes for both.
2. Add and configure a Calculated Value control.
   - Name and Title = Days Between
   - Formula = dateDiffDays(Date2,Date1)
        - Click on the Formula Builder button to the right of the Formula field.
        - Go to the Runtime Functions tab and add the dateDiffDays function to the Formula.
        - Go to the Named Controls tab and add inside parentheses Date2,Date1
        - Click OK to add the formula.     - 
   - Connected to = Name of your list column to save the date difference (if needed)
   - Save the Calculated Value control configuration.
3. Add and configure the Reason for Delay control.
4. Add and configure a Rule to the Reason for Delay control.
   - Select the Reason for Delay control.
   - Click on the Add Rule button in the ribbon.
   - Configure the Rule.
        - Rule name = Require Reason for Delay
        - When = greaterThan(Days Between, 22)
             - Click on the Formula Builder button to the right of the When field.
             - Go to the Runtime Functions tab and add the greaterThan function to the Formula.
             - Go to the Named Controls tab and add inside parentheses Days Between control.
             - Complete the formula by adding ,22 
             - Click OK to save the formula.
        - Then = Invalidate
        - Validation Message = Reason for Delay required