Hi,

You should be able to do this by defining a custom event for insert/update on the custom field. 

Edit: 

Here’s a sample online sql to check for negative values: 

BEGIN

  IF (&NEW:CF$_TEST2 < 0 ) THEN

      IFSAPP.ERROR_SYS.Record_General('CustomerOrder','The input value cant be negative. Please adjust the value entered before saving.');

   END IF;

END;

Thanks,

Kasun