Measure for count of last 7 days

I am looking for DAX that will count the number of Visits for the given time frame (today looking 7 days back). I have tried the below, but it is giving me an error regarding duplicate dates. Any ideas?

Requested Last 7 Days = CALCULATE (
        COUNT ( 'Active Assignments'[assignment_seq] ),
        DATESINPERIOD ( 'Active Assignments'[date_requested], LASTDATE ( 'Active Assignments'[date_requested] ), -7, DAY )
    )