need help modifying this cumulative dax formula

I am having trouble getting this formula to reset every month as it doesn't go to 0 but when I have it reset each year it works fine:

Business cumulative = 
SUMX(
    FILTER(
        ALLSELECTED(Opportunity[CreatedDate].[date]),
        Opportunity[CreatedDate].[date]<=MAX(Opportunity[CreatedDate].[date])
        && MONTH(Opportunity[CreatedDate].[date])= month(max(Opportunity[CreatedDate].[date]))
        )
        ,[business days]
    )

If I literally just change out "month" for "year" in this formula it works for a yearly cumulative but it never works on the month level. Here is what happens when I try the formula above:

I changed the formula around so now it resets every month but it gives me a descending cumulative sum?

Business cumulative = 
SUMX(
    FILTER(
        ALLSELECTED(Opportunity[CreatedDate].[date]),
        Opportunity[CreatedDate].[date]>=MAX(Opportunity[CreatedDate].[date])
        && month(Opportunity[CreatedDate].[date])= month(max(Opportunity[CreatedDate].[date]))
        )
        ,[business days]
    )