calculate difference in days between two dates

use Convert value action. In Input field use Inline function DateDiffDays by insert reference:

when i user the below function, and updated, i'm getting the same which i user inside function like fn-daysdiffdates(date1, date2) only, it not executing andgivin the results. i thing i'm doing wrong, please let me know correct way of getting the difference in lik days-hours format