Year over Year script isn't working please help

[J7House1984]

I am working on a dashboard and I am showing a box with Previous year data. Below is what I have come up with, however I am getting either an error message. or a message of no data. The data I am testing definitely has data. If I input the year I want such as 'Date', 'Date'[Year] = 2020 it will give me the data I am looking for. Am I missing something or not doing something correctly. Please help.

GetValueFromPrevYearSelected =

VAR _SlicerYearValue = SELECTEDVALUE('Date'[Year])

VAR _Result =

CALCULATE(

SUM('GA - RHM Summary'[New Users]),

FILTER(

'Date', 'Date'[Year] = (_SlicerYearValue) - 1

)

)

Return

_Result