You need to set the validator values for both the minimum and maximum to work, so do a furmula for the minimum like this:

 

@Adjust(@Today(), 0, -1,0,0,0,0);

And then set the maximum to something way out of range like 3001/01/01

 

Set the error message to something understandable like "Date is not valid / must be one month ago or newer."

 

Good coding

Newbs