Time duration

[Tim_Mao]

I am trying to filter messages in my app for “last week”. this following error message really puzzles me.

Arithmetic expression ‘((TODAY()-[_THISROW].[Sent Date/Time]) < 7)’ does not have valid input types

[Sent Date/Time] is the date time type marks the time a message sent out. I am trying to build an expression in Slicing the messages table.