Measure to count a category by month (+ criteria) to visualize in a line chart - not break line

[joyc0025]

How can I create a DAX measure to display the count of approved orders by month?

• The filter is Activity Type = “EME” and Decision Code = “Approve”
  The legend is by Business Unit (which is in a related table).
• The measure only counts for the month range of 12 months prior to the date in the slicer which is in an related table ''Date_Workflow Approvals'[Date]
• Month’s with no count should have +0 so the chart doesn't show broken lines
• Ideally any business unit with no count in the filtered date range should be excluded entirely but this is proving difficult and no longer a main priority.
• The chart needs to have a filter enabled on Decision Code and Activity type so it can be passed via  drill through to a table showing the supporting data.
  
  Table: Workflow Approvals
  Table: Purchasing Location
  Date Table:
  

  
  Unrelated slicer date table: 'Date_Workflow Approvals'

  

  
  I think i'm close with the following:
   - but when i put on the chart filter for PO Activity type = "EME"  (for drill through to data), it breaks the lines 

Approval EME Count YTD = 
VAR EndMonth =
    MAX ( 'Date_Workflow Approvals'[Date] )
VAR StartMonth =
    EOMONTH ( EndMonth, -12 )
VAR SelectedMonth =
    MAX ( 'Workflow - All Approvals'[Month] )
RETURN
    IF (
        SelectedMonth >= StartMonth
            && SelectedMonth <= EndMonth,
        CALCULATE (
            COUNT ( 'Workflow - All Approvals'[Order Number] ),
            'Workflow - All Approvals'[Decision Code] = "Approve",
            'Workflow - All Approvals'[PO Activity Type] = "EME",
            'Workflow - All Approvals'[Month] >= StartMonth
                && 'Workflow - All Approvals'[Month] <= SelectedMonth
        ) + IF(ISBLANK(SelectedMonth) && NOT ISBLANK(StartMonth), 0, 0),
        BLANK ()
    )

I've spent hours going in circles with ChatGPT but getting nowhere..