Group over dates and count max value

File attached.

Best

D

Yeah... You're almost there. I've given you the full description:

# Invoices =
// Get the latest date visible in
// the current context from a DISCONNECTED
// table of dates.
VAR __selectedDate = MAX ( Dates[Day] )
// Harvest the currently visible steps from
// a DISCONNECTED slicer.
VAR __selectedProcessingSteps =
	VALUES ( Step[Processing Step] )
VAR __invoices =
    // Get a table of (unique) invoice numbers that
    // adhere to the conditions of the task.
    CALCULATETABLE (

    	FILTER (
            // In the current context, get the unique invoice numbers.
            VALUES ( 'Invoice Processing'[InvoiceNumber] ),
            // For each invoice number returned by VALUES,
            // find the max TimeOrder and get the corresponding
            // processing step. There will be only one due to
            // the uniqueness of the combination (InvNo, TimeOrder),
            // so VALUES (in __step) will return only one value that will then
            // be automatically converted by DAX into a scalar.
            VAR __maxTimeOrder =
            	// Calculate is needed here to perform context transition.
                CALCULATE ( MAX ( 'Invoice Processing'[TimeOrder] ) )
            VAR __step =
                // For the above max TimeOrder get the corresponding
                // process step. Also, this works correctly due to
                // context transition. As I said above, the outcome
                // will be a single item.
                CALCULATE (
                    VALUES ( 'Invoice Processing'[ProcessStep] ),
                    'Invoice Processing'[TimeOrder] = __maxTimeOrder
                )
            RETURN
                // For the invoice being iterated, check if
                // the latest step is in the selected steps.
                // This is because there can be many steps
                // visible - think: the total in a table/matrix.
                __step
                    IN __selectedProcessingSteps
        ),
        
        // Filter the invoice processing data for the records where
        // the selected date falls between the start and end date;
        // this will be applied first for CALCULATETABLE so that
        // FILTER can "feel" it and only see the relevant rows.
        // Pay attention to the type of the inequalities as it's
        // crucial to get the correct numbers.
        'Invoice Processing'[StartDate] <= __selectedDate,
        (
            __selectedDate <= 'Invoice Processing'[EndDate]
                || ISBLANK ( 'Invoice Processing'[EndDate] )
        )
    )
VAR __invoiceCount =
    COUNTROWS ( __invoices )
RETURN
    __invoiceCount

Best

D