Number of Open items per calendar week

I have a transaction table in which invoices and payments are saved, each with the date of the transaction. The document number is the same for an invoice and the associated payment.

I would now like to display the outstanding invoice amounts per calendar week and how many different invoices are still open.
I have displayed the open amount using this DAX formula. But how do I calculate the number of invoices concerned?

still open = sum of Amount per DocumentID != 0

In my opinion, the difficulty lies in the fact that you can only recognize that the voucher is still open if the total per voucher number is 0.

Transactions:

DateTypeDocumentIDAmount

Calendar:

Calendar = 
ADDCOLUMNS (
    CALENDAR (
        DATE ( 2023, 1, 1 ),
        DATE ( 2023, 12, 31 )
    ),
      "YYYYWW", FORMAT ( [Date], "YYYY" ) & Format ( WEEKNUM ( [Date], 21 ), "00" ),
    "WW/YY",
        CONVERT ( WEEKNUM ( [Date], 21 ), STRING ) & "/"
            & FORMAT ( [Date], "YY" ),
    "DateKey", FORMAT ( [Date], "YYYYMMDD" )
)

Measure for Amount until today:

Amount until today = 
CALCULATE (
    SUM ( Transactions[Amount] ),
    'Calendar'[Date]<= MAX ( 'Calendar'[Date] ),
    ALL ( 'Calendar' )
)

Thank you!