Help with Dashboard

Hello everyone, 

I am trying to develop a dashboard, I have main sales table, each entry in this table has a date with only month and year. I want to show the data using cards and slicers on the main visualization. The first slicer is for brands, the second slicer is for month and year and the last slicer is the end scale.

Brand slicer: user can select the particular clothing brand he wants to see the data for

Month_year slicer: user can select the particular month and year he wants to see the data for

Endscale slicer: user can select the timeframe he wants to go back from the particular month and year value he selected from the month_year slicer

For example, the user can select that he wants to see the sales for Nike, for the month of September and year 2022 and he selects the endscale as 6 months, this means he will see the last six months of data starting from September 2022.

These are the two slicer that I have created. The endscale slicer comes from a table that I have created which is not connected to any table. The month_year slicer comes from the Calendar table that I have created which is connected to the main sales table with a column by the same name as month_year. 

This is the calendar table with 3 other calculated columns that I made.  I also made a measure to display the total sales like I described in the Nike example above, this is what the measure is:

testing = 

VAR endscale_selection = SELECTEDVALUE('Time'[Endscale])
VAR y = SWITCH(endscale_selection, "R03", 2, "R06", 5, "R12", 11)
VAR month_selection = SELECTEDVALUE('Calendar'[Month_Year])

VAR start_date = DATE(YEAR(month_selection), MONTH(month_selection),   DAY(month_selection))
VAR end_date =   DATE(YEAR(month_selection), MONTH(month_selection)-y, DAY(month_selection))
VAR x = CALCULATE(SUM(Sales[Dollars]),   
                  FILTER(
                      'Calendar', 'Calendar'[Month_Year]>= end_date && Calendar[Month_Year]<= start_date
                  )
                )
RETURN x

In the above code I am trying to display the sales of a particular brand based on the slicer selection for timframe/endscale, the particular month_year combination and the particular brand. But for some reason the card which holds this measure is just showing a "Can't Display this visual" message. 

I am also attaching the image of my table model for reference(removed some things due to privacy):

Any suggestions would help a lot, as to how can I make it work.

Thanks in advance.